Household Hazardous Waste

Science of the Total Environment 337 (2005) 119 – 137 www.elsevier.com/locate/scitotenv

Review

Household hazardous waste in municipal landfills: contaminants in leachate R.J. Slacka, J.R. Gronowb, N. Voulvoulisa,* a

Department of Environmental Science and Technology, Imperial College, Prince Consort Road, London, SW7 2BP, UK b Environment Agency, Block 1, Government Buildings, Burghill Road, Westbury-on-Trym, Bristol, BS10 6BF, UK Received 13 November 2003; received in revised form 10 June 2004; accepted 2 July 2004

Abstract Household hazardous waste (HHW) includes waste from a number of household products such as paint, garden pesticides, pharmaceuticals, photographic chemicals, certain detergents, personal care products, fluorescent tubes, waste oil, heavy metalcontaining batteries, wood treated with dangerous substances, waste electronic and electrical equipment and discarded CFCcontaining equipment. Data on the amounts of HHW discarded are very limited and are hampered by insufficient definitions of what constitutes HHW. Consequently, the risks associated with the disposal of HHW to landfill have not been fully elucidated. This work has focused on the assessment of data concerning the presence of hazardous chemicals in leachates as evidence of the disposal of HHW in municipal landfills. Evidence is sought from a number of sources on the occurrence in landfill leachates of hazardous components (heavy metals and xenobiotic organic compounds [XOC]) from household products and the possible disposal-to-emissions pathways occurring within landfills. This review demonstrates that a broad range of xenobiotic compounds occurring in leachate can be linked to HHW but further work is required to assess whether such compounds pose a risk to the environment and human health as a result of leakage/seepage or through treatment and discharge. D 2004 Elsevier B.V. All rights reserved. Keywords: Xenobiotic organic compounds; Heavy metals; Municipal solid waste disposal; Endocrine disruptors; Pharmaceuticals; Pesticides

1. Introduction Household waste, any waste produced from a domestic source, represents over two-thirds of the municipal solid waste (MSW) stream (OECD, 2001). Internationally, almost 70% of MSW is disposed of to * Corresponding author. Tel.: +44 207 594 7459; fax: +44 207 594 6016. E-mail address: [email protected] (N. Voulvoulis). 0048-9697/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2004.07.002

landfill (OECD, 2001; Zacarias-Farah and GeyerAllely, 2003). MSW contains hazardous substances in the form of paints, vehicle maintenance products, mercury-containing waste, pharmaceuticals, batteries and many other diffuse products which are discussed in the review paper by Slack et al. (2004). Unlike the waste streams originating from industrial sources, hazardous substances in household waste are not strictly controlled under hazardous waste regulations such as the US Resource Conservation and Recovery

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Act 1976 (RCRA) and the European Hazardous Waste Directive 91/689/EEC (US Code, 1976; European Council, 1991). As such, household hazardous waste (HHW) is disposed of to landfill along with general household waste. The amounts and significance of this disposal are poorly understood. Generally, it is assumed that amounts are small and therefore risks of disposal are negligible. Nevertheless, disposal information is lacking or, at best, unreliable and ambiguous. Changes to legislation requiring the separate disposal of MSW, industrial and other wastes, raises the importance of the hazardous element contained in MSW. Previous studies have found that, even without landfill co-disposal, leachates from MSW are very similar in composition to those from mixed or hazardous landfills (Schrab et al., 1993; Kjeldsen et al., 2002). Emissions from landfill take a number of forms: gaseous emissions of volatile organic compounds (VOCs), airborne particulate matter and leachate. The contamination of groundwater by landfill leachates has been recognised by a number of researchers (Christensen et al., 2001; Kjeldsen et al., 2002). Leakage potential may be mitigated by a number of factors, many enshrined in legislation, including landfill capping. In Europe, the recent Landfill Directive has further enforced the treatment of emissions from landfill sites (European Council, 1999). The European Council Decision setting out the criteria and procedures for waste acceptance at landfills (European Council, 2002) utilises the leaching limit values for the three landfill types listed in the Landfill Directive (European Council, 1999). Only MSW and separately collected non-hazardous fractions of household wastes, according to Chapter 20 of the EWC, can be considered non-hazardous without testing. Failure of any of the engineered control measures can result in the release of a cocktail of chemicals, as reported by Schwarzbauer et al. (2002). For older landfills, the implementation of measures to prevent release to the environment is less well defined with the result that aquifer contamination was far more common as were elevated levels of localised VOCs (Reinhard et al., 1984). Leachate treatment and discharge also possesses risks to the environment through ineffective treatment and/or discharge to particularly sensitive receiving waters (Silva et al., 2004).

Whilst leachate contamination of the groundwater environment is less likely from modern landfills as a consequence of engineered barriers and leachate collection, the risk still exists. Knowledge of leachate composition is necessary for the implementation of site remediation following barrier breakdown and for installation of practicable treatment processes. Although major components of landfill leachate, especially ammonical nitrogen, can be predicted with some certainty using models to predict the possible typical leachate resulting from the deposition of generic waste groups, the trace composition of leachate is inherently variable due to the heterogeneity of specific waste composition and other factors relating to the landfill (Reinhart, 1993; Robinson, 1995; Blight et al., 1999). Leachate composition is also an indication of the types of waste disposed and the processes occurring within the landfill. The presence in leachate of heavy metals and hazardous organic contaminants, such as halogenated aliphatic compounds, aromatic hydrocarbons, phenolic compounds and pesticides, are direct indicators of the disposal of hazardous wastes in MSW (Christensen et al., 2001; Kjeldsen et al., 2002; Isidori et al., 2003). However, care must be taken with MSW leachate analyses that reveal the presence of harmful substances due to the codisposal of industrial liquid wastes and manufacturing wastes with MSW. The co-disposal of hazardous and non-hazardous wastes is a practice soon to be banned in EU Member States through the implementation of the Landfill Directive, effective from July 2004 (European Council, 1999). The consequences of HHW disposal are therefore obscured in many leachate studies. Where it is possible to differentiate waste sources, leachate composition has the potential to act as a useful tool in HHW risk evaluation. As concern about chemicals in household products increases (Blundell, 2003), the potential consequences to the environment from the disposal of HHW are also moving to the fore. It is therefore important to ascertain the level of risk inherent in the disposal of HHW to landfill, as permitted by current legislation. This work focuses on the analysis of the possible routes for environmental contamination from which the risks to environment and human health can be evaluated. A review of leachate

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analyses together with an assessment of landfill biogeochemistry permits extrapolation from leachate contaminant back to HHW disposal, with leachate composition potentially acting as an indicator for landfill discarded HHW. The contamination risks associated with the disposal of HHW at each stage of the disposal-to-landfill-to-emissions pathway have not been examined in detail before.

2. Landfill leachate composition Leachate contains inorganic and organic elements. Xenobiotic organic compounds (XOCs) and heavy metals are generally classified as the hazardous substances occurring in leachate. Hazardous XOCs and heavy metals can be toxic, corrosive, flammable, reactive, carcinogenic, teratogenic, mutagenic and ecotoxic, among other hazards, and can also be bioaccumulative and/or persistent. MSW landfill leachate analyses permit identification of the commonly found XOCs and heavy metals derived from waste with a domestic origin. Extrapolation back to the original source is often possible, allowing the risks of discarding certain wastes to landfill to be assessed. Environmental and human health risks arise from exposure to hazardous substances in groundwater, surface water, gaseous emissions and dust evolution as a result of leakage through the barriers of new engineered landfills, dispersal from older landfills without barriers or as a result of ineffective leachate or gas treatment prior to discharge. However, the types of waste discarded do not solely determine leachate composition. Conditions existing within the waste body also contribute to the type of landfill emissions. Chemical and biological transformations of the waste and interactions of plant-derived matter and XOCs/heavy metals, influenced by the various redox phases undergone through the life of a landfill, affect emissions at any point in time (Robinson and Gronow, 1993). To fully assess the risk of landfill disposal of HHW, the life span of the landfill requires continual monitoring and leachate analyses. If the phases are well understood, as indicated by the extensive literature concerning conditions within the landfill, then it is possible to dmapT the degradation of particular waste streams and the possible emissions that result.

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XOCs derive directly from the waste discarded to landfills. However, conditions within the landfill determine the final composition of leachate. Biodecomposition of putrescible waste increases general levels of dissolved organic carbon (DOC) (Reinhard et al., 1984). The higher the levels of DOC, the greater the elution through sorption to organic matter of hydrophobic XOC pollutants such as phthalate esters (Bauer and Herrman, 1997; Bauer et al., 1998; Oman and Rosqvist, 1999). DOC concentrations also affect the mobility of metals (Van der Sloot, 1998; Meima et al., 1999). Ammonical nitrogen is produced in much higher concentrations than XOCs with levels consistent across the different landfill phases (Robinson and Gronow, 1993; Christensen et al., 2001). Whilst not classified as hazardous, ammonical nitrogen has the potential to act as one of the dominant environmental pollutants produced from landfills containing putrescible wastes and hence poses problems for the management of all landfills. It has frequently been described as the most frequent pollutant of groundwater, emanating from landfills at concentrations of greater magnitude than other emissions (Christensen et al., 2001; Barlez et al., 2002; Baker and Curry, 2004). Biological or chemical transformations in the solid phase or leachate can lead to the formation of toxic substances from relatively innocuous organic compounds. 1,4-dioxane (Yasuhara et al., 1997), a controlled substance, could result from such a transformation, whilst carbon tetrachloride, another toxic compound, is a principle constituent of PVC (Health and Safety Commission (HSC) 2002). Results from various studies reveal different degrees of degradation for a variety of XOCs under the various redox conditions found within and adjacent to the landfill, as reviewed by Kjeldsen et al. (2002). As anaerobic conditions persist in capped landfills, any leachate plume progresses from strongly reducing methanogenic conditions in the landfill through the progressively weaker reducing redox zones marked by sulphate, iron and nitrate reduction to aerobic conditions in the aquifer (Reinhard et al., 1984; Read et al., 2001). Various of the compounds found in HHW have been dmappedT through these zones such that determination of the specific degradation patterns and interactions is possible. Dichlor-

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oethene and vinyl chloride are examples of the chlorinated solvents attenuated in the anaerobic conditions by abiotic redox environments and the biotic microbes found therein (Bradley and Chapelle, 1996; Bradley and Chapelle, 1997). The low levels of chlorinated organic compounds generally detected in leachates result, at least partially, from the reductive dechlorination of hazardous compounds, such as polychlorinated biphenyls (PCBs), during the acid formation and methanogenic phases within the landfill (Reinhart and Pohland, 1991). The aromatic hydrocarbons exemplified by the BTEX compounds (benzene, toluene, ethylbenzene and xylenes) can degrade under aerobic conditions but demonstrate little anaerobic degradation activity, raising the possibility of groundwater contamination, particularly in the case of benzene (Nielsen et al., 1996; Christensen et al., 2001). Phenols and pesticides often demonstrate contradictory behaviour regarding degradation in anaerobic and aerobic conditions. Pentachlorophenol is reported to degrade in anaerobic conditions (Kjeldsen et al., 1990) but the pesticide mecoprop resists degradation under anaerobic conditions, which helps to explain its common occurrence in leachate analyses (Heron and Christensen, 1992; Rugge et al., 1999; Williams et al., 2003). Schwarzbauer et al. (2002) reported that phthalates and other plasticisers do not significantly decline in either anaerobic or aerobic conditions. The heavy metal content of leachate shows a reduction from acid phase to methanogenic phase due in part to increased sorption to DOC and metal precipitation with sulphates and carbonates (Robinson and Gronow, 1993; Christensen and Christensen, 1999; Christensen et al., 2001; Kjeldsen et al., 2002). Work by Suna Erses and Onay (2003) found that 90% of all heavy metals present in a landfill simulation were attenuated within 10 days of methanogenic onset through heavy metal precipitation. The application of heavy metal balances to landfills has revealed that less than 0.02% of heavy metals disposed of to landfill are leached within the first 30 years of the lifespan of the landfill due to metal immobilization by organic/inorganic sorption and precipitation (Belevi and Baccini, 1989; Flyhammer, 1995). For instance, mercury in landfills is predominately found as an insoluble sulphide precipitate and is therefore resistant to leaching. However, it is

reported that the anaerobic conditions of modern landfills may encourage the biomethylated transformation of mercury into more soluble and volatile methyl mercury (Jones and McGugan, 1978; Compeau and Bartha, 1985), with the result that Lindberg et al. (2001) argue that landfills may be a dominant source of atmospheric mercury. However, the Environment Agency for England and Wales report that volatile mercury has not been detected above toxicity thresholds in gaseous emissions, determining loss from landfills predominantly through adsorption to particulate matter released as dust (Parker et al., 2002). Transformations and degradation of the waste types disposed to landfills can cause landfill-discarded waste to become more-or-less hazardous. Landfill processes should therefore be considered when assessing leachate composition, described in the following section. Tables 1 and 2 include many of the chemicals identified in leachate from MSW landfills that possess hazardous properties, several of which can be traced back to their original waste source through consideration of the reactions occurring within the waste body of the landfill. 2.1. Organic compounds More than 200 organic compounds have been identified in municipal landfill leachate (Yasuhara et al., 1997; Paxe´us, 2000; Schwarzbauer et al., 2002), with upwards of 35 compounds having the potential to cause harm to the environment and human health (Paxe´us, 2000). More than 1000 chemicals have been identified in groundwater contaminated by landfills generally (Christensen et al., 2001; Kjeldsen et al., 2002). The majority of these compounds are derived from decomposing vegetation and degradation products of natural materials (Reinhard et al., 1984; Schwarzbauer et al., 2002), with cellulose and hemicellulose alone comprising up to 60% of the total dry weight of MSW (Barlaz et al., 1989). Such compounds, aliphatic and aromatic acids, phenols and terpenes, have a tendency to degrade as any leachate plume migrates from a site (Reinhard et al., 1984; Leenheer et al., 2003). Ammonical nitrogen and dissolved organic matter, as total organic carbon (TOC), biochemical oxygen demand (BOD) and chemical oxygen demand (COD), encompass the

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primary organic degradation products (Robinson and Gronow, 1993; Christensen et al., 2001; Kjeldsen et al., 2002). A large number of the degradation compounds can be described as XOCs and result from the disposal of waste containing BTEXs, chlorinated aromatics, chlorinated/non-chlorinated hydrocarbons, nitrogencontaining compounds, alkylphenol ethoxylates and alkyl phosphates (Schwarzbauer et al., 2002). Table 1 lists selected XOCs frequently identified in landfill leachate. Types and concentrations of XOCs differ across leachates studied, from dilute (Ag/l) to concentrated (mg/l), a reflection of the differences in landfill age, waste composition and landfill management processes occurring at the site (Oman and Rosqvist, 1999; Christensen et al., 2001). Benzene, toluene, ethylbenzene and xylenes (BTEX compounds) are found in the highest concentrations reflecting their common usage as solvents in a range of products and waste generating processes, along with the halogenated hydrocarbons tetrachloroethylene, trichloroethylene and dichloroethanes (Reinhard et al., 1984; Krug and Ham, 1991; Kjeldsen, 1993; Christensen et al., 2001; Kjeldsen et al., 2002). Table 1 demonstrates their almost universal occurrence in leachate. These compounds, aside from being among the simplest to analyse for, have been designated US Environmental Protection Agency priority pollutants based on aquatic pollutant capability (Kjeldsen et al., 2002). The occurrence of plasticisers in leachate has been widely reported (Bauer and Herrman, 1997; Bauer et al., 1998; Mersiowsky et al., 2001; Yamamoto et al., 2001; Mersiowsky, 2002; Jonsson et al., 2003; Marttinen et al., 2003). Principle among this group of compounds are phthalates, of which di-(2-ethylhexyl)phthalate (DEHP), diethyl phthalate (DEP), diisononyl phthalate (DINP) and dibutyl phthalate (DBP) have been extensively used in the manufacture of consumer goods (Mersiowsky, 2002; Schwarzbauer et al., 2002). Nevertheless, other phthalates are commonly recorded in both co-disposal and MSW landfill leachates, as shown in Table 1. The degradation product, phthalic acid, has generated the highest leachate concentrations, levels reaching 14 mg/l (Kjeldsen et al., 2002). Concern for these compounds has developed over recent years due to their classification as endocrine disruptors (Jobling et al., 1995;

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Fukuoka et al., 1997) and phthalates, as phthalic acid esters, are listed as dpriority pollutantsT by the US EPA (Keith and Telliard, 1979). A tendency to persist in the environment and bioaccumulate in organisms are the main contributory factors to their priority status (Schwarzbauer et al., 2002). Xenoestrogens are metabolites of various widely used substances that are preferentially adsorbed onto sewage sludge (Marcomini et al., 1989), suggesting one possible entry route to landfill. Other plasticisers, phosphates and sulphonamides, are also categorised as environmental pollutants (Albaiges et al., 1986; Oman and Hynning, 1993). Robinson failed to detect significant levels of DEHP in 26 leachate samples and concluded that plasticisers were not considerable contaminants of leachate in the UK at the time (Robinson, 1995). Bisphenol A (4,4V-(1-methylethylidene)bisphenol), originating from plastics and epoxy resins, acts as an oestrogen mimic (Krishnan et al., 1993). It is also a common contaminant of landfill leachate in some countries, often occurring at high detection levels (Yasuhara et al., 1997; Yamamoto et al., 2001; Schwarzbauer et al., 2002; Coors et al., 2003). Landfill leachates in Sweden have been identified as sources of other endocrine-disrupting substances found in aquatic ecosystems (Noaksson et al., 2003). The occurrence of pharmaceutical products in landfill leachate has also been reported, with propyphenazone, ibuprofen and clofibic acid identified in leachate leaking through the faulty bottom seal of a domestic landfill in Germany (Schwarzbauer et al., 2002). Holm et al. (1995) describe the rapid methanogenic degradation of a group of pharmaceuticals in groundwater contaminated by landfill leachate including propyphenazone, sulphonamides and barbiturates. Phenazone, an analgesic similar to propyphenazone, was identified in soil and groundwater below a MSW landfill by Ahel and Jelicic (2001). Eckel et al. (1993) further identified pentobarbital in groundwater from a landfill. Work by Schecker et al. (1998) investigated the elimination of ifosfamide, a cytostatic drug falling under the auspices of the European Waste Catalogue (European Commission, 2000), from a sanitary landfill. Approaching 50% of the ifosfamide added to a methanogenic landfill was eliminated after 120 days. More general assessments of groundwater contamination not necessarily linked to landfill seepage have identified a greater variety of products

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Table 1 Xenobiotic organic compounds frequently found in MSW and co-disposal landfill leachates with a possible origin in HHW Compounds

CAS no.

Use

Presence in HHW

Landfill type and reference

Halogenated hydrocarbons Bromodichloromethane

75-27-4

X

2

Chlorobenzene 1,4-Dichlorobenzene 1,3-Dichlorobenzene

108-90-7 106-46-7 541-73-1

X Y X

1, 3, 5, 8, 15 1, 3, 5, 7, 8 1, 7, 8

1,2-Dichlorobenzene

95-50-1

Y

1, 3, 5, 7, 8, 15

1,2,3-Trichlorobenzene 1,2,4-Trichlorobenzene 1,3,5-Trichlorobenzene

87-61-6 120-82-1 108-70-3

X/Y X/Y X/Y

1, 2, 7 1, 2, 7, 8 2

Hexachlorobenzene

118-74-1

X

1

Hexachlorobutadiene

87-68-3

X

2

1,1-Dichloroethane

75-34-3

X/Y

1

1,2-Dichloroethane

107-06-2

Y(old)

1, 2, 7, 8

Tribromomethane

75-25-2

X

2

1,1,1-Trichloroethane

71-55-6

Y

1, 2, 3, 5

1,1,2-Trichloroethane

79-00-5

X/Y

1

1,1,2,2-Tetrachloroethane

79-34-5

X/Y

1

trans-1,2-Dichloroethylene

156-60-5

X/Y

1

cis-1,2-dichloroethylene

156-59-2

X/Y

1

Trichloroethylene

79-01-6

Y(old)

1, 2, 3, 5, 8

Tetrachloroethylene Dichloromethane

127-18-4 75-09-2

X Y(old)

1, 2, 3, 5, 8 1, 5, 7, 8

Trichloromethane

67-66-3

X

1, 5, 7, 8

Carbon tetrachloride

56-23-5

Y

1, 2, 8

Chloroethene

75-01-4

Chlorinated water, some as manu. substrate Industrial solvent and substrate Toilet-deodorisers and mothballs Insecticide/fumigent; chlorophenol substrate Pesticide, manu. substrate, deodoriser, solvent Insecticide, substrate, solvent Insecticide, substrate, solvent Chemical intermediate, explosives, pesticides Industrial by-product of solvent, pesticide and wood preservation Manu. of rubber/lubricants and industry Paint solvent, degreasant, breakdown of 1,1,1-trichloroethane Vinyl chloride manufacture: paint, adhesives, pesticides and cleaning products: solvent to remove petrol lead. Degreasent and substrate—no longer used Solvent esp. paint and adhesive; cleaning products and aerosols Solvent, unknown use: 1,1,2,2-tetrachloroethane breakdown product Industrial solvent and substrate: was used in paint, pesticides and degreasant Solvent and manu. (pharmaceuticals, etc.) Solvent (perfumes, etc.) and manu. (pharma, etc.) Solvent, substrate, degreasant: solvent in tipp-ex, paint removers, adhesives and cleaners Dry-cleaning and degreasant Solvent in paint stripper, aerosols, cleaners, photographics, pesticides Solvent and substrate: forms from Cl in water All uses stopped? No longer a refrigerant, etc. Used for plastics? Plastics and vinyl production—house, drugs, etc.

Y

8

Aromatic hydrocarbons Benzene

71-43-2

Y

1, 2, 3, 5, 6, 7, 8, 13, 15

Multitude of uses—manufacturing of dyes, pesticides, drugs, lubricants and detergents

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Table 1 (continued) Compounds

CAS no.

Use

Presence in HHW

Landfill type and reference

Aromatic hydrocarbons Toluene

108-88-3

Y

1, 2, 3, 5, 7, 8, 13, 15

Xylenes

1330-20-7

Y

1, 2, 3, 5, 6, 7, 8, 13, 15

Ethylbenzene

100-41-4

Y

1, 2, 3, 5, 8, 13, 15

Trimethylbenzenes

N/A

X/Y

1, 3, 5, 8, 13

n-Propylbenzene t-Butylbenzene Ethyltoluenes Naphthalene

103-65-1 98-06-6 e.g. 622-96-8 91-20-3

X X X Y

1, 1, 1, 1,

2-Methylnaphthalene

91-57-6

Y

3, 7, 8, 13, 15

1-Methylnaphthalene

90-12-0

Solvent in paint, paint thinners, nail varnish, etc. Plastics manu.: solvent in paints, nail varnish Pesticides, varnishes, adhesives and paints Solvent, substrate (paint, perfume, dye), fuel Solvent and manu. Solvent and manu. Solvent and manu. Moth repellent, toilet deodoriser, manu. of dyes and resins Insecticides, chemical intermediate (dye/vit. K) Insecticides, chemical intermediate (dye/vit. K)

Y

3, 7, 8, 13, 15

Phenols Phenol Ethylphenols

108-95-2 90-00-6

X/Y X/Y

1, 2, 3, 5, 6, 7, 12, 13, 15 1, 3, 15

Cresols

1319-77-3

Y

1, 3, 5, 6, 7, 12, 13, 15

Bisphenol a

As phenol

Y

1, 6, 7, 15

Dimethylphenols 2-Meth/4-methoxyphenol

105-67-9 90-05-1/50-76-5

X(Y) Y

1, 12, 15 1

Chlorophenols

95-57-8

X(Y)

1, 7, 12, 13, 15

2,4-Dichlorophenol

120-83-2

Y

7

3,5-Dichlorophenol

591-35-5

Y

1

Trichlorophenols

N/A

X/Y

15

2,3,4,6-Tetrachlorophenol Pentachlorophenol

58-90-2 87-86-5

X Y(old)

1, 15 2, 15

Polychlorinated biphenyls

1336-36-3

X

2

Alkylphenols Nonylphenol Nonylphenol ethoxylate

104-40-5 9016-40-9/NA 31

Surfactants Detergents, wetting/dispersing agents, emulsifier

X/Y X/Y

1, 15 15

Pesticides Aldrin/dieldrin Ametryn

309-00-2/60-57-1 834-12-8

Banned insecticides Herbicide

X X

2 1

Slimicide, disinfectant, drugs and manu. Solvent, naturally occurring in some foods Wood preservatives, drugs, disinfectant and manu. Manufacture of epoxy resins, coating on food cans? Solvent Manu. antioxidants, drugs, plastics, dyes: flavouring Pesticides, antiseptics, manu., Cl-treated water Manu. herbicides, PCP: mothballs, disinfectant Manu. herbicides, PCP: mothballs, disinfectant PCP and organochlorine pesticide metabolites Pesticides, wood preservative Wood preservative no longer used in households Transformers and capacitors: b1970s used in consumerables paint, adhesives, fluorescent lamps, oil, WEEE

8, 13 8 8, 13 3, 5, 6, 7, 8, 13, 15

(continued on next page)

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Table 1 (continued) Compounds

CAS no.

Use

Presence in HHW

Landfill type and reference

N/A 1912-24-9 25057-89-0 1698-60-8 101-21-3 50-29-3 {72-54/55-8/9}

Glyphosate Herbicide—US licenced Herbicide Pyridazinone herbicide Carbinilate herbicide Banned insecticides

X Y X X X X

1 2, 7 1 1 1 2

Dichlobenil Dichlorvos N,N-Diethyltoluamide Endosulfan (a/h) Endrin Fenpropimorf Glyphosate Hexazinon Hydroxyatrazin Hydroxysimazin Isoproturon g-Hexachlorocyclohexane Malathion Mecoprop Methyl parathion MCPA Propoxur Simazine Tridimefon 4-CPP 2,4-D 2,4,5-T 2,4-DP

1194-65-6 62-73-7 134-62-3 33213-65-9 72-20-8 67564-91-4 1071-83-6 512-350-42 2163-68-0 NA 1063 34123-59-6 581-89-9 121-75-5 7085-19-0 298-00-0 94-74-6 114-26-1 122-34-9 43121-43-3 3307-39-9 94-75-7 93-76-5 120-36-5

Herbicide Insectide (indoor) and veterinary care Insecticide (body) Insecticide and wood preservative No longer used (insect/rodent/avicide) Morpholine fungicide Herbicide Non-agricultural herbicide Atrazine metabolite Simazine metabolite Phenylurea herbicide Insecticide and lice treatment Insectide, flea and lice treatment Herbicide Insecticide—agricultural Herbicide Acaricide/insecticide Herbicide Fungicide Herbicide Herbicide Herbicide (agent orange) Herbicide (alongside mecoprop)

Y Y Y X X X Y X X X X Y Y Y X Y X Y X X Y X Y

1 2 6 2 2 1 1 1 1 1 1 1, 2 2 1, 4, 5, 6, 13, 14 2 1 1 2 1 1 1 1 1

Phthalates Monomethyl phthalate Dimethylphthalate Diethyl phthalate

– – 84-66-2

Y Y Y

1 1, 7 1, 4, 5, 6, 7, 9, 15

Y Y

1, 9 1, 9

Pesticides Ampa Atrazine Bentazon Chloridazon Chlorpropham DDT {DDD, DDE}

Methyl-ethyl phthalate Mono-(2-ethylhexyl) phthalate Di-(2-ethylhexyl) phthalate Mono-butylphthalate Di-n-butylphthalate

– –

Plastics Plastics All plastic consumerables, insecticides, drugs, cosmetics Plastics Plastics

117-81-7

All plastics including medical ware

Y

1, 6, 7, 9, 10, 15

– 84-74-2

Y Y

1, 9 1, 5, 6, 7, 9, 15

Di-isobutylphthalate Mono-benzylphthalate Butylbenzyl phthalate Dioctylphthalate Phthalic acid Diheptyl phthalate

– – 85-68-7 117-84-0 N/A 3648-21-3

Plastics PVC plastics and nitrocellulose lacquers (varnish) Plastics Plastics Plastics All plastics, pesticides and cosmetics Phthalate breakdown product Plastics

Y Y Y Y Y Y

1, 1, 1, 1, 1, 7

6, 9 9, 6, 6,

9 15 15 10

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Table 1 (continued) Compounds

CAS no.

Use

Presence in HHW

Landfill type and reference

Aromatic sulphonates Naphthalene sulphonates Benzene sulphonates p-Toluenesulphonate

– 68411-30-3 80-40-0

Azo dyes, detergents, plasticisers Azo dyes, detergents, plasticisers Azo dyes, detergents, plasticisers

Y Y Y

1 1 1

Plasticiser and intermediates Plasticiser

Y Y

6 6, 15

Sulphones and sulphonamides Diphenylsulphone 127-63-9 N-Butylbenzene 3622-84-2 sulphonamide Phosphonates Tributylphosphate Triethylphosphate

126-73-8 78-40-0

Plasticiser, solvent, antifoaming agent Plasticiser, solvent, antifoaming agent

Y Y

1, 3, 5, 6, 15 1, 3, 6, 7, 15

Terpenoids Terpenoids (general) Borneol

N/A 507-70-0

Y Y

11 6

Camphor 1,8-Cineole Fenchone Limonene Menthol Pinene a-Terpineol Tetralins Thymol

76-22-2 470-82-6 e.g. 1195-79-5 5989-27-5 15356-70-4 e.g. 80-56-8 98-55-5 N/A 89-83-8

Plant by-product, chemical intermediate Chemical, perfume, flavouring intermediates Perfume and incense additive Flavours and fragrance Flavouring Flavouring Flavours and fragrance Flavours and fragrance Flavours and fragrance Flavours and fragrance Flavours and fragrance

Y Y Y Y Y Y Y Y Y

1, 3, 5, 6, 8, 13, 15 3, 6 1, 3, 6, 13 3 15 6, 7 15 6

Pharmaceuticals Ibuprofen Propylphenazone Phenazone Clofibric acid

15687-27-1

Anti-inflammatory/analgesic-OTC

Y

6

479-92-5/60-80-0 882-09-7

Analgesic—rarely used today Plant growth reg. and drug intermediate

X Y

6, 15 6

Pyridines Methylpyridine (2–?)

109-06-8

X

6

Nicotine Cotinine

54-11-5 486-56-6

Solvent and substrate for dyes, resins, drugs Insecticide, tobacco Formed from oxidation of nicotine

X/Y X/Y

1, 6 6

Carboxylic acids Benzoic acid

65-85-0

Phenylacetic acid Benzenetricarboxyl acids Palmitic acid Stearic acid Linoleic acid Aliphatics n-Tricosane n-Triacontane

Y

3, 6, 15

103-82-2 e.g. 528-44-9 57-10-3 57-11-4 60-33-3

Food preservative, perfumes, creams/drugs, manu. Fragrance/flavour, drugs (penicillin) Plastic softeners Food, cosmetics and pharmaceuticals Food, cosmetics and pharmaceuticals Food and fragrance

Y Y Y Y Y

3, 3, 3, 3, 3,

638-67-5 638-68-6

Plastics and intermediate Intermediate

X X

6, 7 6, 7

6 6 6, 15 6, 15 6

(continued on next page)

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Table 1 (continued) Compounds

CAS no.

Use

Presence in HHW

Landfill type and reference

Alcohols and ethers Glycol ethers

e.g. 111-76-2

Y

6

General alcohols Diphenylethers

N/A 101-54-8

Solvent {paint, varnish, inks, pesticides, antifreeze} Solvents Flame retardant, plasticiser, herbicide

Y Y

1 6

Aldehydes and ketones Aldehydes

N/A

Y

1, 6

Ketones

N/A

Solvents {plastics, paints}, stain remover Preservative, resin/dye manu., intermediate

Y

1, 6

Miscellaneous Acetone

67-64-1

Y

1

Analines

N/A

X/Y

3, 6, 7

Benzonitrile

100-47-0

Y

3, 4, 7, 15

Benzthiazoles

N/A

Y

6, 7

Dibenzofuran

13-26-49

X

7

Caffeine Esters Tetrahydrofuran

58-08-2 110843-98-6 109-99-9

Y Y Y

1, 7 6, 15 1

Indane Indene Indoles

90989-41-6 95-13-6 N/A

Y Y Y

1, 6 8 6, 15

MTBE

1634-04-4

X(Y)

1

Siloxanes

N/A

Y

6, 15

Styrene

100-442-5

Y

8, 15

Trifluralin

158-20-98

Solvent and in manu. of plastics, drugs and fibres Ink/dye, resins, drugs, agrochemical intermediate Solvent: dye, drugs, rubber, lacquer manu. Manu. of drugs, rubber, agrochemicals, etc. From fossil fuel combustion—incl. Diesel fuel Food additive, drugs Many uses during manufacture Food additive, reagent (drugs, perfumes), solvent Fuel and metal cleaning Solvent and intermediate Intermediates, food colourant, drugs/hallucinogenics, perfumes, etc. Solvent used as additive in unleaded petrol Silicone polymers—varnish, oils/waxes, rubber Naturally occurring, used for plastics/rubber manu. Herbicide

X

2

Presence in HHW: X=non-municipal/household use, Y=municipal/household use, X/Y=either/or but generally non-municipal/household use, X(Y)=non-municipal/household but possibly occurring in MSW, Y(old)=no longer used in municipal/household products but possibly occurring in MSW. Landfill types: (1) co-disposal landfills cited by (Kjeldsen et al., 2002); (2) MSW landfills although co-disposal likely in all (Robinson, Gronow, 1993); (3) co-disposal landfills (Reinhard et al., 1984); (4) simulation using household waste (Oman and Rosqvist, 1999); (5) co-disposal landfill (Christensen et al., 2001); (6) no details supplied (Schwarzbauer et al., 2002); (7) co-disposal landfill (Yasuhara et al., 1997); (8) codispoal landfill (Zou et al., 2003); (9) mixed landfills receiving different wastes (Jonsson et al., 2003); (10) simulation using household waste (Bauer and Herrman, 1997); (11) MSW landfill (Leenheer et al., 2003); (12) co-dispoal landfill (Ask Reitzel and Ledin, 2002); (13) co-disposal landfill (Baun et al., 2003); (14) co-disposal landfill (Lyngkilde and Christensen, 1992); (15) co-disposal landfill (Paxe´us, 2000).

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Table 2 Heavy metal concentration ranges detected in landfill leachates Metal

Use

Concentration range (mg/l)

US drinking water standards (mg/l)

UK drinking water standards (mg/l)

References

Cadmium Nickel

Batteries, appliances Batteries, appliances

0.0001–0.4 0.0036–13

0.005 N/A

0.005 0.05

Zinc Copper

Batteries, packaging Electrical appliances

0.003–1000 0.002–10

5 1.3

5 3

Lead Chromium

Batteries, appliances Electrical appliances

0.001–5 0–1.62

0 0.1

0.05 0.05

Mercury Arsenic Cobalt

Batteries, appliances Appliances Appliances

0.00005–0.16 0.01–1 0.005–1.5

0.002 0 N/A

0.001 0.05 N/A

(Christensen et al., 2001) (Christensen et al., 2001; Kruempelbeck and Ehrig, 1999) (Christensen et al., 2001) (Christensen et al., 2001; Jensen and Christensen, 1999) (Christensen et al., 2001) (Jensen and Christensen, 1999; Robinson, 1995) (Christensen et al., 2001) (Christensen et al., 2001) (Christensen et al., 2001)

(Jones et al., 2001) such as the analgesics diclofenac and ketoprofen (Heberer et al., 1997; Sacher et al., 2001); antibiotics sulfamethoxazole, dehydroerythromycin and sulfamethazine (Hartig et al., 1999; Hirsch et al., 1999); the antiepileptic drug carbamazepine (Seiler et al., 1999; Schwarzbauer et al., 2002); and the h-blocker sotalol (Sacher et al., 2001). Pesticides and herbicides are frequently recorded in MSW landfill leachate. N,N-Diethyltoluamide (DEET), bentazon, MCPA and particularly mecoprop (2-(4-chloro-2-methylphenoxy)propionic acid) are common and persistent in anaerobic landfill conditions (Schultz and Kjeldsen, 1986; Gintautas et al., 1992; Lyngkilde and Christensen, 1992; Kjeldsen, 1993; Oman and Hynning, 1993; Christensen et al., 2001; Kjeldsen et al., 2002). Christensen et al. (2001) and Kjeldsen et al. (2002) cite the discovery of at least a further 40 different pesticides in landfill leachate, including the Red Listed aquatic pollutants atrazine and simazine (Alloway and Ayres, 1997), with the most frequently occurring being listed in Table 1. Naphthalene and related compound contamination of leachate is also commonly reported (Reinhard et al., 1984; Yasuhara et al., 1997): this compound is a recent addition to the UK’s Approved Supply List (Health and Safety Commission (HSC), 2002), a classification system applied to chemicals considered to be dangerous. 2-Butylphenyl methylcarbamate (BPMC) and benthiocarb have also been detected (Yasuhara et al., 1997). Detergent surfactants are reported from leachate analyses, particularly sulphonates and alkylphenol

polyethoxylates (Riediker et al., 2000; Kjeldsen et al., 2002). Such surfactants occur in laundry detergents and personal care products, although the latter surfactant, particularly as nonylphenol ethoxylates, is not commonly used due to concerns over environmental and health problems, especially endocrine disruption (Jobling and Sumpter, 1991). Nevertheless, nonylphenol has been reported to be present in municipal landfill leachate in some countries (Paxe´us, 2000; Behnisch et al., 2001; Coors et al., 2003). Synthetic musks, used to fragrance detergents and personal care products, are reported to possess toxic capabilities and, although not yet monitored in leachate, have been recorded in sewage receiving waters in a number of countries, but first found in Japan (Yamagishi et al., 1981, 1983; Ford, 1991; Daughton and Ternes, 1999). Other significant representative xenobiotic compounds distinguishable in leachate include more chlorinated organics (Reinhard et al., 1984; Yasuhara et al., 1997; Paxe´us, 2000; Schwarzbauer et al., 2002) such as pentachlorophenol, one of many such compounds considered to be a dpriority pollutantT by the US EPA (Pohland et al., 1998). 2,4-Dichlorobenzoic acid, together with other chlorinated aromatics including benzene and methylphenol, occur in varying quantities in leachate (Schwarzbauer et al., 2002). Leachate concentrations of chlorofluorocarbons (CFCs) tend to be low compared to other organic compounds due to high rates of attenuation (Reinhart and Pohland, 1991; Hohener et al., 2003). Even so, CFCs have been recorded as gas and leachate

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emissions from MSW landfills in Germany and through Canadian landfill simulations (Lesage et al., 1993; Deipser and Stegmann, 1994), predominantly in the acid phase before the onset of methanogenesis but detail about concentration and volume is lacking (Hohener et al., 2003). Whilst CFCs possess a low level of toxicity in the aquatic environment, their breakdown products are more reactive and inherently more toxic or carcinogenic (Hohener et al., 2003). Complex fractions containing nicotine and benzthiazol together with their oxidation products (Schwarzbauer et al., 2002) and caffeine (Albaiges et al., 1986) are common contaminants of leachate, often existing at high concentrations in the German and Spanish landfills studied. Kjeldsen et al. (2002) highlight the discovery of levels of the gasoline additive methyl-tert-butyl-ether (MTBE) found at significant concentrations in some Swedish landfills. Dioxanes (glycol ethylene ether) such as 1,4-dioxane and dioxolans, originating from alkyd resin production wastes and discarded paint and similar products, are reported to occur in MSW leachate from Japanese and Swedish landfills (Yasuhara et al., 1997; Paxe´us, 2000). Robinson, however, failed to detect many dRed ListT substances (Department of the Environment, 1988) in any of the landfill leachate samples collected across England and Wales: other hazardous substances were detected at very low levels (Robinson, 1995). Although concentrations of XOCs are only a small fraction of the total carbon content of leachate, the levels observed in a multitude of studies indicate that concern for aquifer contamination is justified (Albaiges et al., 1986; Lyngkilde and Christensen, 1992; Kjeldsen, 1993; Kjeldsen et al., 1998; Christensen et al., 2001; Schwarzbauer et al., 2002). With water quality levels in many countries set as low as 0.1 Ag/l for certain XOCs, the concentrations achieved in leachate may therefore be perceived as a potential threat to public health if incorrectly managed (Kjeldsen et al., 2002). 2.2. Inorganic components The inorganic element of leachate has been studied alongside organic constituents (Yasuhara et al., 1997). Heavy metals found in the inorganic fraction are of particular interest due to their hazardous nature

(European Commission, 2000). Commonly occurring heavy metals in landfill leachate include zinc, copper, cadmium, lead, nickel, chromium and mercury (Reinhart, 1993). Heavy metals can form metal colloids or complexes, particularly with organic matter, removing the metal from direct detection as free metals (Gounaris et al., 1993; Christensen and Christensen, 1999; Jensen and Christensen, 1999). As such, the heavy metal content of leachate can be significantly higher than free metal detection studies allow, and calculations based solely on the water solubility constants of the pollutants will underestimate their concentrations (Jonsson et al., 2003). Generally heavy metals, demonstrating high levels of sorption and precipitation, do not constitute a groundwater pollution threat due to poor migration into the leachate plume and low initial concentrations leached from the solid waste (Table 2). Heavy metals can, however, reach problematic levels despite depressed concentrations relative to other substances evolved into the leachate. Ehrig (1983), Kjeldsen et al. (2002) and Robinson (1995) found that heavy metal levels, particularly mercury and cadmium, in domestic waste landfill leachate are barely detectable and pose little threat to groundwater. Zinc, however, is usually recorded at concentrations orders of magnitude greater than other heavy metals (Christensen et al., 2001). Heavy metal contamination of aquifers is almost exclusively as soluble high molecular weight organic complexes. Such contamination of groundwater can be of environmental and potable drinking water concern, as the drinking water standards provided in Table 2 demonstrate (Reinhard et al., 1984). This concern is heightened by the identification of concentrations of heavy metals exceeding legislative permits in leachate sampled in the USA and Eastern Europe, including drinking water limits shown in Table 2 (Lu et al., 1985; Mikac et al., 1998). Even with the maximum permissible levels for heavy metals as high as 5 mg/l (US Drinking Water Standard for zinc), weak leachate concentrations can often approach this limit (Kjeldsen et al., 2002). Nevertheless, particulate matter contaminated with heavy metals has been cited as one of the primary sources of heavy metal emissions from landfills (Parker et al., 2002). Other contaminants of landfill leachate can be referred to as inorganic macrocomponents (Christen-

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sen et al., 2001). As occurs for dissolved organic matter and the less concentrated subgroup xenobiotic organic compounds, inorganic macrocomponents occur at much higher concentrations compared to heavy metals. Iron and manganese fall into this group as they cannot be considered to be heavy metals, along with calcium, sodium, potassium, ammonia/ ammonium and others. Ammonical nitrogen (ammonia and/or ammonium) is recorded at high levels in most landfill leachate studies with Robinson (1995) and Kjeldsen et al. (2002) both describing it as the dominant pollutant.

3. Landfill gas During the methanogenic phase of landfill decomposition, many of the degradation products resulting from waste decomposition in the acid anaerobic stage can be volatised from the leachate (Christensen et al., 2001). As a result, landfill gaseous emissions can contain similar hazardous compounds to the leachate. Whilst the dominant proportion of landfill gas is methane (~50–60%) followed by carbon dioxide (~ 40%), many trace VOCs are also released (Kreith, 1995). VOC emissions, including saturated and unsaturated hydrocarbons, acidic hydrocarbons and organic alcohols, aromatic hydrocarbons, halogenated compounds and sulphur compounds as identified in leachate, can present health and environmental concerns (Kreith, 1995). Zou et al. (2003) identified up to 60 VOC species in one landfill, 16 compounds of which were US EPA priority pollutants including benzene and derivatives, and chlorinated hydrocarbons and aromatics. Specific compounds occurring at higher levels, although together rarely exceeding 1% v/v, were naphthalene, chloroform, carbon tetrachloride, trichloroethane and chlorobenzene as well as benzene. The volatile heavy metals, arsenic and mercury, have been detected at trace levels in landfill gas, although association with particulate matter has been demonstrated to contribute more to the emissions of heavy metals from landfills (Parker et al., 2002). Allen et al. (1997) recorded over 140 VOCs, whilst James and Stack (1997) and Assmuth and Kalevi (1992) found 33 and 30 VOCs, respectively, with benzene

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in the former study and carbon tetrachloride in the latter being recorded at levels in excess of guideline limits. However, the comprehensive sampling strategy reported by Parker et al. (2002) identified 557 trace components in landfill gas, 178 of which are inherently toxic. Nevertheless, levels detected were below statutory guidelines, specifically of the more toxic substances such as mercury.

4. Discussion The composition of leachate is an indicator of the disposal of hazardous waste to landfills. Many of the substances recorded in landfill emissions have the potential to act as environmental contaminants. It is important to recognise the potential contribution made by hazardous waste from a domestic origin to landfill emissions particularly in light of the growing and ever-changing variety of chemicals used within the home (Blundell, 2003). Results of numerous studies indicate that the range and amounts of hazardous substances present in leachate from MSW landfills, while only a fraction of the total organic and inorganic content of leachate, can be seen to approach the drinking water standards set by many countries (Mikac et al., 1998; Gendebien et al., 2002; Kjeldsen et al., 2002; Schwarzbauer et al., 2002). Leachate is a consequence of water entering the landfill and leaching biological and chemical components from the body of the waste. When evaluating the disposal of HHW, the conditions within the landfill must be acknowledged to determine the nature of the components and the likelihood of occurrence in leachate. Substances not found in HHW at disposal can occur in leachate as a result of degradation and other transformations. Quantities of hazardous substances will vary according to landfill conditions, particularly moisture content and ionic strength of the leachate. Charting the contamination of groundwater through leakage requires not only knowledge of the leachate composition as it left the landfill, but application of the attenuation processes known to affect leachate in sub-surface strata (Christensen et al., 2001). It is only possible to ascertain the presence of particular substances selected for by the experimen-

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tal design (Isidori et al., 2003). The sampling procedure may easily overlook certain groups of hazardous components and hence their contaminant capability will remain unevaluated. Synthetic musks are one such group thus far untested in landfill leachate and yet identified in sewage receiving waters. The quantities of the hazardous chemicals so far detected in leachate vary from study to study, from trace levels to amounts exceeding established limits. Such variation is the result of differences in disposal practice, levels of regulation, landfill design and ultimately a reflection of the purchasing patterns of consumers (market forces, availability, culture, etc.) in different countries. Alternatively, sampling error might play a significant role through the inappropriate application of certain methodologies and analytical techniques (Parker, 1994; Paxe´us, 2000; Kjeldsen et al., 2002). As XOCs and heavy metals occur at trace levels, accurate quantification is often difficult. The heterogeneity of landfills also complicates sample selection. Landfill age is an important contributory factor and as Robinson (1995) explains, leachate composition is variable over time and hence analyses should incorporate a time axis. The affects of the hazardous fraction of MSW on leachate composition in all but a very few of the studies reviewed here (see Tables 1 and 2) have been obscured through the co-disposal of industrial and manufacturing wastes with MSW. Table 1 reveals that many of the MSW landfills are in fact co-disposal sites, industrial and manufacturing solid and liquid wastes having been integrated into the domestic refuse. The hazardous compounds linked directly to MSW are therefore few in number and variety, a reflection of the limited number of compounds analysed for and the use of experimental landfill simulations (Oman and Rosqvist, 1999). The pesticide mecoprop and phthalates DEHP and DEP are the substances most commonly linked to MSW (Gintautas et al., 1992; Bauer et al., 1998; Jonsson et al., 2003). Whilst a large proportion of the XOCs listed in Table 1 and all of the heavy metals from Table 2 are found in household products, the significance of the contribution made by MSW or even household waste to the final leachate make-up is uncertain. It can be supposed that certain of the substances, particularly

some solvents, will be present in barely detectable amounts in the absence of industrial waste (Baxter, 1985). Other chemicals, exemplified by phthalates, may maintain the concentrations recorded in codisposal leachates. Recent changes to legislation may make it possible to observe a change in leachate composition as co-disposal of hazardous with non-hazardous waste ceases and domestic landfills accept non-hazardous wastes only (European Council, 1999). With increasing EU-led legislation implementing regulations on product composition and disposal practices, such as the Restrictions on Hazardous Substances in Electrical and Electronic Equipment (RoHS) Directive and the Waste Electrical and Electronic Equipment (WEEE) Directive (European Parliament and Council, 2002a, b), leachate from existing and new landfills can be expected to be very different to that of older/closed sites, with the potential for a rapid decline in the landfilling of biodegradable substances and a resulting shift in landfill-contained chemical processes. The consequences for the hazardous component of MSW requires further evaluation, although a decline in organic matter through implementation of the Landfill Directive can be expected to result in leachates containing predominantly inorganic ions and a consequent change in leachate treatment techniques. The impact of DOC sorption on XOC and heavy metal attenuation may similarly be reduced. Current European legislation tends to the treatment of all landfill emissions preventing many of the potentially hazardous substances from entering the environment at large. As a result, the pollution risk is allayed to a variable extent. Methane is often used for electricity generation, whilst leachate is currently treated in systems comparable to sewage treatment works. Use of ozonation plants and UV radiation are increasingly recognised as effective additions to leachate and wastewater treatment operations given the low efficiency of conventional processes regarding chemical removal. As a result, pesticide, pharmaceutical and even phthalate removal (Bauer et al., 1998) will increase, possibly reducing the likelihood of groundwater contamination by these substances. However, such measures are costly and unlikely to occur unless specific legislative drivers are in place, particularly for

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MSW landfills. Other risk mitigation measures applied to landfill leachate include combinations of biological processes, coagulation/precipitation, adsorption and membrane processes, all of which utilise the physical, chemical and biological properties of the hazardous substances (Enzminger et al., 1987). Research also cites the benefits of traditional treatment using microbial anaerobic decomposition (Pohland, 1991; Staples et al., 1997; Gavala et al., 2003; Jonsson et al., 2003). However, a need for more non-biological techniques for leachate treatment is predicted. A comprehensive understanding of the wastes disposed of, the underlying landfill processes and, the emissions from landfills, now and in the future, can contribute to the assessment of the economic and environmental necessity of taking such steps. Further work is required to quantify the amounts of hazardous substances emitted from MSW landfill and ascertain the links to HHW disposal. Leachate concentrations can potentially act as a guide to amounts of the hazardous substances disposed in household waste and provide an indication of the chemical pathways operating/occurring within the landfill body. The risks from the release of such substances into the surrounding environment, either as a result of leakage or through insufficient leachate treatment, require assessment to evaluate the potential harm to health and the environment from continued disposal of HHW to landfill. Prioritization of the most harmful will enable waste managers to provide the most appropriate leachate treatment options on identification of the hazardous substance, or permit alternative disposal practices to be developed. As more waste is diverted from landfill, it will be important to assess how this will affect HHW disposal and potential leachate toxicity.

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disposal pathway, particularly when conditions and processes within the landfill are understood. The awareness of the waste types disposed of is insufficient for determination of leachate composition without subsequent consideration of the fate and behaviour of hazardous substances within the body of the landfill. Leachate is a consequence of the waste types disposed and the conditions prevalent within the body of the landfill determining degradation/transformation processes. Data relating directly to MSW or household waste landfill sites are few, with most information deriving from co-disposal landfills. The analytical techniques applied to leachate samples can also impose limitations on the determination of the contaminants arising from HHW. As co-disposal of hazardous industrial waste with MSW is soon to be banned, the impact of the hazardous element of MSW or HHW requires further assessment. The hazardous nature of certain types of MSW has the potential to rival certain industrial wastes as pollutant risks. The changing state of legislation also will impact on HHW behaviour within landfills and the quantities of HHW disposed to landfill. Further work in this area is needed to clarify the origins of the MSW leachate contaminants recorded and the possible affects of legislatively driven changes to landfill management on landfill composition. Crucially, the risks to environment and human health from HHW disposal to landfills requires further attestation through the quantification of emissions and likelihood of release after leachate/gas treatment or as a consequence of leakage or seepage. This latter point is needed before further legislation relating to HHW disposal to landfills, such as the WEEE Directive, is considered. References

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