Issues in risk assessment of compost from municipal solid waste: occupational health and safety, public health, and environmental concerns

Biomassand Bioenqy Vol. 3, Nos Printed in Great Britain. All rights

3-4, pp. 145-162, 1992 reserved

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0961-9534/92 $5.00 + 0.00 1992 Pergamon Press Ltd

ISSUES IN RISK ASSESSMENT OF COMPOST FROM MUNICIPAL SOLID WASTE: OCCUPATIONAL HEALTH AND SAFETY, PUBLIC HEALTH, AND ENVIRONMENTAL CONCERNS JAMES W. GILLETT

Institute for Comparative and Environmental Toxicology, 16 Femow Hall, Cornell University, Ithaca, NY 14853-3001, U.S.A. (Received 22 May 1992; accepted 7 July 1992)

Abstract-Risks posed by cornposting of municipal solid waste (MSW) depend on the assessment approach used. Occupational risks at present are not overtly serious-only nausea, eye irritation, etc. are reported from inhalation, the chief exposure pathway-but details are lacking on outcomes of pathogenic, chemical and physical threats, including potential secondary problems with organisms developedin compost, their endotoxins, and metabolic products such as aflatoxin. Potential risk pathways of public exposure to MSW compost are dominated by children’s lead ingestion, but “dioxins” and other persistent organic carcinogens are also of dietary concern. Risks to the “most exposed individual” (MEI) may differ substantially from those based on the Alternative Pollutant Limit (APL) approach. Neither deals adequately with uncertainty or multiple pathway/chemical threats to public and environmental health. Additional issues include (a) incremental vs. total risk, (b) required nutrient intake vs. proscribed toxicant exposure (for the same element) and (c) long-term matters of “no net degradation,” and composting in recycling. Keywords--Municipal

solid waste, compost, hazard, exposure, occupational assessment, metals, organics.

1. OVERVIEW

Disposal of municipal solid wastes (MSW) has raised questions about public health and environmental safety and, to a considerably lesser degree, occupational health and safety of workers involved. Approaches used in MSW disposal have evolved as critics identified serious problems with each successive method. The transition from open dumps to (in some cases) incineration has resulted in increased costs and technical difficulties in response to these concerns. These economic and health forces have led to a structured set of priorities’-waste minimization, reuse/recycling, incineration, and secure landfill/deposition-in handling the high volume of tremendously heterogeneous MSW arising in urban areas. Much of the MSW stream is organic, and composting of this material ranks high on the waste hierarchy, usually as a subset of recycling. In addition to traditional components of the MSW stream (kitchen and yard waste, packaging, worn out items of everyday living), other waste streams (wastewater sludges, incinerator fly ashes, manures, and food processing wastes) vie for use in production of compost and other soil amendments.

The standard approaches to such questions of risks include a case-by-case examination of the waste stream for potentially hazardous substances, a component-by-component analysis of the changes in their nature and concentration brought about by waste treatment, estimation of concentrations to which various vulnerable targets might become exposed by pathways originating in a given process or use of the material, and comparison of the time-dosage exposure profile of these toxicants to known adverse effect dosage-responses of human and environmental targets. The overall methodology and individual aspects regarding specific wastes, toxicants, and jurisdictions are under the scrutiny of several agencies, so that the interactions between the scientific communities of several disciplines, agencies at various levels of government, and numerous proprietary interests are being blended in seeming cacophony.2 The U.S. Environmental Protection Agency (U.S.E.P.A.)’ has focussed on the “most exposed individual” (MEI) in a set of hypothetical scenarios employing “conservative” (upper bound or upper 95% percentile) estimates, parameters, etc., intended to protect the populations at risk by evaluating the outcomes of 145

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very high exposures in the laboratory and extrapolating to human populations exposed at very low levels. This conservative approach may or may not be protective but may restrict or prohibit management practices which have very low (unknown?) risks. Another evaluation strategy has been invoked by advocates of useful products from waste.4 This procedureAlternative Pollutant Limits (APL)‘-focuses on use of realistic exposure scenarios and emphasizes pragmatic field data regarding uptake, distribution and impact, while deemphasizing laboratory-based and hypothetical concerns centered on the MEI. The intent is to identify clearly the patterns of exposure likely to have unacceptable risk while delineating those where risks are nominal or de minimis. If waste management practices can be ascertained to yield products in which testing fails to evoke adverse effects at a de minimis or “no-observable-adverse-effect-level” (NOAEL), then that material presumably can be used in an unrestricted manner. The exposure assessment relies upon producing composts by “best available technology” and applying them to soils at reasonable rates as per “best management practice”, on standardized dietary and physiologic variables in food consumption, and on measured (rather than assumed) exposure parameters. A third approach, not yet applied to composts in a regulatory context, is emerging from the APL and similar analyses of waste management and Superfund site remediation. Rather than generate point estimates of risk using the ME1 or APL, simulation technology can be employed to use the full range and shape of available data to estimate the frequency with which critical risk values are likely to be exceeded.6*7 For heterogeneous materials and circumstances, exposition of the full range of outcomes by what has been termed “uncertainty analysis”’ is likely to offer the most advantageous insight. At the same time, however, it is necessary to convince regulators and the regulated communities of its value and validity.’ The plethora of laws and federal, state and local agencies make development and enforcement of risk-based standards, however, anything but simple. Assessed exposure and hazard may be viewed by some as if a bright line existed between “safe” and “unsafe”. Chaney, Gillett and othersg*” have complained that numerous assumptions by U.S.E.P.A. and its contractors regarding health and environmental

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risks assessments have used values arbitrarily, without regard to whether the specified combination of conditions and risks can exist. At the same time, the presumption of safety for exposures within the lower 95% confidence interval ignores needs of populations in the upper 5% of exposures.8 Any discussion of the risks presented by MSW compost must evoke a broader analysis of how we make decisions, carry out actions intended to be protective of health and the environment, and conserve materials and natural resources, so that limited resources are used most effectively.” In addition, there are technical policy questions. Exactly how should these risks be considered-as part of total risk or only incrementally? How does one resolve overlap between levels of nutrient need (Recommended Daily Allowance, RDA) and presumably toxic levels proscribed by other agencies (Reference Dose, RfD; Cancer Potency Value, Q,*)? Does compost as a disposal method have a different legal status than compost as a recycling use? Does recycling via compost over time present threats not evaluated for compost as a simple, linear process (e.g., a pollutant moving from MSW to a compost to a crop compared to the same set of processes continued by crop residues and food wastes being returned to the soil as compost from garbage and thence back to human consumption)? How does the combined action of the multi-pollutant mixture in MSW compost affect assessment? These issues may or may not be relevant to any particular composting process, facility and/or product; in toto they need a reasoned and timely response from a host of professionals, politicians, and the public. This article reviews the status of these issues, 2. OCCUPATIONAL

HEALTH

AND SAFETY (OHS)

In the press to respond to the crisis in MSW management, much more attention has been devoted to potential adverse health effects for the general public and on wildlife than with regard to workers in the MSW composting industry.‘* For example, there is a dearth of insurance actuarial information on worker injury and disease. Attitudes of many concerned with general, consumer or public health hazards of MSW appear to be rather blase regarding OHS. This lack of attention appears to stem from the presumption that, however MSW is handled, the workers will either be protected by standing OHS rules and practices or liabilities

Risk assessment issues for MSW compost

will be reduced by appropriate management by the responsible contractor/agency. Whether or not MSW cornposting will be mandated or even approved has not appeared to rest on any impacts on workers. Contrary to the foregoing, however, there are a significant number of hazards involved in cornposting of MSW,13 particularly arising from the presence of human feces and other sources of pathogens, endotoxins from bacteria, and various organics and inorganics in dusts. Documented experience in Europe’2,‘4 is especially helpful in providing insight into the issues. Attention to OHS of the procedures and products of the composting process has largely been directed at the incremental effect of any exposure. Workers in MSW industries have not been as fortunate as those in other manufacturing and production areas, because the level of skill/education can be minimal, workers are seldom organized, and the public has been inclined to look the other way and ignore the full costs of waste management. Hence, the risks and consequent costs of occupational hazards in waste management activities have received little attention in the rush to adopt or adapt technologies in response to perceived threats from past waste management actions. OHS in manufacturing industries, on the other hand, has become increasingly sophisticated as a management field, and many heretofore “dangerous” occupations now have exemplary records. Although costs are typically passed along to the consumer, management and workers alike see OHS programs as creating a more effective and efficient working environment in which worker concerns are answered successfully while external and internal liability costs are contained. Higher retention/lower turnover, improved worker satisfaction, and less loss of time on the job are the secondary benefits with direct implications for ultimate operational costs. Where skilled occupations are involved, both unions and managements have been involved in training, job design, etc.” Risk management is also considered to be more easily performed in the work place, in that training, use of equipment and techniques, monitoring of the workers and the work place, and cost implications can be more readily incorporated into facility, process, and product design and their associated activities. The risk assessment paradigm applied to OHS generally follows that explicated by the National Research Council.‘6

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(a) Hazard identification-determination of the nature of potential stressors and the insult(s) they present, including sensitivities in special populations or previously stressed groups; (b) Hazard assessment--determination of a dose-response-time profile for the stressor; (c) Exposure assessment-determination of the time-dosage profile presented to the potentially stressed population; (d) Risk characterization-evaluation of the interaction of the exposure and hazard assessments under realistic conditions of appropriate scenarios for the “average” and “maximally exposed individual” (MEI); and (e) Risk assessment-comparison of the risk characterized above to societally derived risk goals, standards or guidelines, taking into account the many factors impinging on subsequent actions taken to minimize any risks thus noted. In general, occupational risks are evaluated within a more narrow context than those for the general population and specifically assume an adult-only exposure period of 40 h/week, 50 weeks/year for a 30-year working lifetime. Because workers are presumably compensated for some of these risks, “accepted” risks are commonly lo-fold greater than those of the general public. Risks can be grouped into those which are de minimis (not meriting further concern), and de manifestis (requiring action regardless of costs because they are so untoward or excessive). Acceptable occupational risks thus span IO-’ to 10m3in terms of morbidity or mortality (or 1 chance in 100,000 to 1 chance in 1000 of being a victim) from a life-threatening impact such as cancer. 3. HAZARD IDENTIFICATION

Any hazards in MSW compost to workers will cover almost all anticipated threats to the public generally. Depending on the process design and the particular steps taken to control the quality of the product, MSW composting has a number of sources of potential exposure to pathogens, toxic substances, and other hazards. These can be summarized as follows: ?? Primary human pathogens, principally in baby and adult disposable diapers and to a lesser degree in the variety of household medical wastes (pus-, vomitus- or mucus-contaminated materials), including viruses, mycoplasmas, bacteria, fungi, and cysts or eggs of intestinal parasites;

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Secondary pathogens and their toxins (spores, endotoxins) generated by bacterial and fungal growth within the composting process itself; ?? Volatile and semi-volatile organic chemicals of both synthetic and natural origin, including noxious odors; a Persistent, Iipophilic organic chemicals; a Metals and other inorganics (e.g., asbestos) and organometallics; ?? Allergens from household and yard wastes; and ?? Corrosive, caustic, and explosive materials and those capable of inflicting trauma (“sharps”). In those instances where municipal or industrial wastewater sludges or other waste products are incorporated into the composting process in efforts to enhance product quality and processing efficiency, more or less emphasis may need to be placed on primary pathogens and chemical contaminants. For the most part, however, since MSW is so diverse, these alternative waste streams do not change the qualitative assessment of hazards, although they could affect the quantitative view of exposure and therefore risk. In addition to the foregoing list, the whole process involves use of equipment and machinery with their own notable hazards not specifically evaluated here. ??

3.1. Primary human pathogens Bacteria and other micro-organisms are typically identified by their growth on selective media under specified conditions/times. This results in clusters of species-perhaps with widely differing virulence and therefore riskbeing co-identified as “fecal coliforms”, “fecal streptococcus”, “hemolytic bacteria”. and “enteric” or “mesophilic” flora. Heavy contamination by fungi and actinomycetes may obfuscate these bacterial determinations, although the latter groups usually require longer incubation periods for full development and identification, by either overgrowing plates or eliciting antibiotics against some or all bacteria present. Viruses are unable to multiply outside of their host cells and are usually assayed via tissue cultures in more costly, technically difficult and non-routine procedures; extraction of viable infective units of viruses is also highly conditional. Protozoans may exist as cysts, and the eggs of various intestinal parasites (or those in other tissues having an intestinal phase or form) may be present.

Studies’* support the conclusion of Clark et al.19 that MSW composting facilities offer about the same range and intensity of human pathogenic organisms as do wastewater treatment facilities, which have been much more intensively studied for a longer period of time. Lundholm and Rylander14 reported numerous gram-negative bacteria (including Acinetobacter calcoaceticus, Klebsiella pneumoniae, Escherichia coli, Acromonas hydrojila, Pseudomonas stutzen, P. syringae, P.juorescens, Serratia sp., Enterobacter cloacae, and E. agglomerans, as well as Proteus vulgaris and P. mirabilis j. Dutkiewicz et al.*’ compiled biohazards for a variety of occupations, including “sewage and compost workers, solid waste (refuse) workers, and agricultural waste workers”; they list hepatitis A virus, Leptospira interrogans, Legionella pneumophilas, Salmonella spp., Mycobacterium xenopi, Entamoeba histolytica and Giardia lamblia. No studies involving the occurrence of organisms of immediate present concern-Mycobacterium tuberculosis and human immunodeficiency virus (HIV)were encountered. Most primary pathogens can be effectively reduced to near zero by the temperature increase accompanying biomass decay and by the relative competitive advantage presented by the substrates available at a given temperature. Thus, many of the gram-negative, mesophilic bacteria and most viruses are virtually eliminated by 45560°C for even a few hours.2’,22 The actinomycetes and fungi (secondary pathogens, v.i.) are, however, promoted by this regime and their mycelia and spores will be present even after growth has ceased due to substrate consumption.‘3 The surety with which prediction of sanitation can be made is affected by two features: (1) temperature, moisture and degree of aeration are unevenly distributed throughout any composting mass, and (2) relatively little information is available about this variation and its implications for microbial survival and recolonization. Strauch24 addressed this problem in part in his detailed review for the European Community. In particular, he was concerned about processing standards as a means of controlling biotic risks, because testing of the sheer mass of compost generated from various wastes at the level of known variation would be infeasible. The U.S.E.P.A has required sewage sludge compost intended for distribution and marketing in agriculture to be held at 40°C for 5 days

Risk assessment issues for MSW compost

at least 4 h at which the temperature is > 55”Cz5 Epstein and Epstein26 concluded that this standard appeared effective in preventing survival of primary pathogens. Schrammeck and Sauerwald2’ (as reviewed by Strauch*‘) had earlier found that both the soils and other amendments with which compost might be used were already as much or more contaminated by primary pathogens. Much of the controversy about effectiveness of pathogen control by cornposting depends upon the assay methods, organisms measured, and the etiology of those organisms (indigenous or added from known laboratory cultures), such that Strauch24 did not concur with de Bertoldi et a1.28 as to the use of Streptococcus faecalis as the best indicator of sanitation. Diverse taxa, including ascarid parasites and pathogenic protozoans, are present in MSW. However, the cornposting process is very adverse to their survival. At the surface, however, conditions may be less destructive and contaminated material may be mixed with sanitized compost, reinoculating it.29 Nonetheless, transmission to workers appears not to have been documented, irrespective of the potential for a variety of serious and even fatal illnesses derived from such organisms, as surveys’4.30 have failed to demonstrate exposure-related infectious disease from primary pathogens among compost workers. Lisk3’ reported finding no pathogenic parasites in any of 26 composts from MSW and/or mixed sludges.

with

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the alveolar sacs or paranasal sinuses where resulting infection may be especially serious and even fataL3’ Exacerbating factors include any immunosuppressive action (tissue transplant drugs, antibiotics, adrenal corticosteroids and certain infections) and a number of disease states, especially those involving pulmonary function.29 Furthermore, asthma victims may develop allergic bronchopulmonary aspergillosis by spore colonization3’ and, if this disease becomes chronic, may be subject to severely debilitating pulmonary disease. A. jlavus also produces aflatoxin, the well-known carcinogen of moldy peanuts and similar grains and forage crops. For both workers on and consumers/users of composts involving human and animal wastes containing either primary or secondary pathogens, the key question therefore becomes “What fungi and bacteria survive to expose workers and eventually consumers in compost?” This is not only a complex question in terms of the time course of survival of groups of organisms during the cornposting process,23 but, as was noted earlier, the answers of which we are aware offer little guidance in predictive risk assessment. 3.3. Volatile and semi-volatile organic contaminants

The basic processes in cornposting involve conversion of organics to CO, and mineralized inorganics (NH,, SO,/SO;*, etc.).32 Many of the low molecular weight compounds can be categorized as “volatile organics chemicals” (VOCs) 3.2. Secondary human pathogens of concern in drinking water, as contributors to the general organic load in the lower atmosThe appearance of a variety of symptoms, ranging from red and irritated eyes to runny phere (thus leading to photochemical smog, nose and nausea,30 implies involvement of dust- ozone and haze), and as part of the workplace borne endotoxins derived from (1) gram- hazard for those involved in MSW on the negative organisms present in MSW or growing tipping room floor. Kissel et al.‘* have estimated in the compost or (2) the large number of that the total concentration of VOCs (ca. actinomycetes and fungi termed “secondary 200 mg m -‘) may reach unacceptable chronic pathogens” produced during the cornposting levels in poorly ventilated acceptance/sorting process. Indeed, the most serious health threat*O areas and thus exceed some recommended actually seems to come from the thermophilic exposures for even non-carcinogenic VOCs. fungus Aspergillus fumigatus and the related A. Of course, lower exposures should be sought flaws, A. carneus, and A. niger. The disease for carcinogenic chemicals present in wastes believed to be caused by A. fumigatus and (e.g., benzene and other aromatics) or produced related spp. is termed “aspergillosis”, “farmer’s as a metabolite (e.g., vinyl chloride from lung”, or “brown lung” and is well known as a polychlorinated ethylenes and ethanes).3Z The product of silage, manure compost, wastewater small amounts of solvents, paints, cleaners and sludge compost, etc. This fungus grows well at related materials in containers in MSW can in 245°C on decaying vegetable matter and thus toto present substantial (but variable and survives most of the cornposting process. The difficulty assessed) exposure once the MSW is resulting spores or conidia can be inhaled into collected and compacted. Pre-sorting and waste

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stream segregation (i.e., by limiting self-hauled input to compost) could easily reduce worker exposure. In addition, many plastics have materials in them-plasticizers, anti-oxidants, UV-inhibitors, dyes, colorants-which will be extracted by such solvents and may be made available for both composting and exposure of workers and the environment. Workers handling the compost itself (and all subsequent consumers) are probably not exposed to the same level and range of these relatively volatile, easily degraded substances. Presumption of ready and complete biodegradability (in which up to 30% of these materials are incorporated into the microbial biomass becoming part of the substance of compost) implies little chronic danger beyond that to workers. Health and safety concerns are often assessed regarding toxicity of individual chemicals with the host of materials present in MSW. However, the diversity and range in scale of such chemicals in MSW practically precludes traditional approaches from establishing a level of safety for exposure to the total load. Workers can be exposed to these chemicals as dusts or vapors which they inhale and/or ingest in the course of MSW and compost manipulation. Some chemicals in the MSW and compost may present an exposure via the skin, either directly or as a result of dust dispersion. Most of the concern centers on on-site worker dust inhalation, especially of bacterial and fungal spores, endotoxins, etc., but the dusts may also carry VOCs and other organic chemicals of concern to workers and consumers. MSW and its compost already have or generate many compounds closely related to VOCs which may contain N, S, or Se and are notable for their strong odor. 29*32 Thiols (including H,S, disulfides, mercaptans and mercaptoethers), aldehydes and amines are the principal detractors of the composting process for both workers and any neighbors of a facility. Many of these also may participate in ozone-generation and haze in the lower atmosphere, but can also act as ozone depletors in the upper atmosphere. During composting, some of these chemicals can be important as sources of nutrients and trace minerals in the compost, but they can also generate toxicants such as nitrosamines, azobenzenes, and other heterocyclics. Most of the malodorous chemicals are VOCs and semi-volatiles (aryl and alkyl amines, sulfides, and aldehydes) originating from anaerobic microbial breakdown of natural ma-

terials. Aerobic composting and the mechanics accompanying aeration reduce the presence of these compounds by volatilization and oxidation over time. Noxious odors may be an alternative source of nausea and headache (attributed to microbes) regarded as a normal and inescapable part of MSW handling, but odors are of significant concern as a general nuisance off-site. To the extent that these odors establish the jobs as very low in esteem, they promote turnover and relegation of these jobs to the most inadequately educated and trained sector of the work force, increasing difficulties in physically managing safety in operations. 3.4. Persistent organics Persistent, lipophilic (fat soluble) organic chemicals include polychlorinated and polybrominated biphenyls (PCBs and PBBs), dioxins and benzofurans, pentachlorophenol from treated wood, and chlorinated aromatics used as sanitizers. Some pesticides will occur as residues in yard or household wastes from legal uses; others may be present because of illegal or thoughtless disposal of containers with significant amounts still in them. Adventitious residues of DDT and related compounds (DDTR), various cyclodiene insecticides (dieldrin and heptchlor epoxide, for example), and lindane are still present, although the products containing them have been banned from sale in the U.S.A. Their presence in household and commercial environments will continue to provide inputs into MSW. Polychlorinated aromatics (PCAs), such as DDT-R and dioxins, as well as aryl amines and some aryl/alkyl phosphotriesters may not be destroyed by the composting process.33 Typically, such chemicals are strongly adsorbed to the organic matrix of recalcitrant natural polymers such as lignins and humic acids and synthetic polymers such as plastics. Past usage and various secondary processes continue to “pump” these compounds from various environmental “sinks”. For example, paper pulp chlorination produces variable amounts of various polychlorinated dibenzofurans and, to a lesser extent, dibenzodioxins. Although the bleach pulp process is being phased out or has already been terminated in many mills, some papers (including recycled materials) may have contained as much as 10m4mg kg-’ of total “dioxins”.34*” Partial combustion of chlorinated phenols (especially the wood preservative pentachlorophenol and sanitizers such as dichlorophenol) or exposure to

Risk assessment issues for MSW compost

alkaline surfaces produces dioxins as well. Because the PCAs are bioaccumulated, they can become food residues, processing wastes, etc. As a class of chemicals PCAs are the major feature of risk assessment for composts and sludges in ocean dumping6 and land applications,35 even though the rate and extent of transfer to organisms from composts, sludges and other wastes is open to question. Almost all of the PCAs are suspected of being carcinogens or at least acting as promoters of carcinogenicity, but relatively few have been sufficiently evaluated so as to provide cancer potency values or other indices of toxicity appropriate to the low levels of chronic exposure. Concerns about acute toxicity or short-term responses-primarily nausea and headacheare not appropriate for PCAs, but responses of the immune system (suppression or activation) and neurophysiologic responses need to be investigated more thoroughly before these potential effects can be judged of no concern. For example, chronic exposure to a number of PCAs produces elevated liver enzyme levels (a factor believed to be tied to their tumor-promoting ability), but no studies of these enzyme levels in compost workers could be found. This type of generic response (hepatic enzyme induction) might be a suitable measure of total exposure.36 A group of chemicals similar to the PCAs, the polyaromatic hydrocarbons (PAHs), are ubiquitous as both anthropogenic and naturally produced compounds. They are in tar from cigarette smoke, soot of burned toast, waste lubricants, cooking oils, and even carbon black of printer’s ink. Only a relatively few of the thousands of these chemicals have been studied regarding cancer and other toxic effects. They are also highly lipophilic and strongly sorbed to the organic matter of the wastes (thus restricting both biodegradation during the cornposting process and later bioavailability), but they do not bioaccumulate as readily as PCAs. Sources of PAHs and some pesticides and plastics can also provide a wide variety of heterocyclic aromatic compounds of serious concern regarding carcinogenicity, neurotoxicity or genotoxicity. This class of chemicals also includes widely studied dyes, drugs and flavoring agents present in small quantities in household wastes as food additives and medicines. Nitroso and azobenzene compounds can be formed in food by cooking or microbial action or during cornposting and result in aromatic heterocyclics.

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A fourth class of relatively recalcitrant organits are aryl and aryl/alkyl phosphotriesters, which are widely used as brake and hydraulic fluids, plasticizers, and flame retardants, in part replacing some of the uses of the now-banned PCBs. These are not volatile, are not nearly as lipophilic as PCBs or PAHs, and may be more or less readily biodegraded when adapted or competent bacteria are present. On the other hand, they are heavier than water and can join other heavier-than-water and water-insoluble substances in creating oily, “non-aqueous phase liquids” (NAPLs) within sediments, soils and even particles of compost. NAPLs might be created by the pressure of compactors or in the mountains of stacked MSW (e.g., landfills), but not much is known about biodegradation and bioavailability of NAPLs in cornposting. Summing up the role of these several classes of persistent organic chemicals in health and safety evaluation of MSW compost is difficult. A large number of adventitious, fat-soluble chemicals may be present in low or variable concentrations expected to increase as biodegradable carbon is removed during composting, but many will be destroyed or be made less bioavailable by cornposting. The exact bioavailability (amount transferred into people consuming compost or fish and wildlife, for example) may be significantly lower than assumed, and some of these chemicals may be activated or increased in toxicity. 3.5. Metals and other inorganics Much attention has been directed at the accumulation of mercury, cadmium, lead, silver, chromium, nickel and other “heavy” metals in compost and subsequently in food crops. The presence of so many source materials-batteries, printing dyes and electronics, to name a few-has been a key issue in process analysis of product safety. 37Although some of these metals share a similar generic reaction with free -SH groups to inactivate certain enzymes, study of the pathologies resulting from exposure of laboratory animals demonstrates the types of problems to be element-specific. Historically, Hg, As and Pb are all recognized as toxic by the public, although these elements have also been used in medicines. In the case of Hg and Cd, epidemiologic studies and severe incidents arising from mobilization of these elements into food have made both professionals and the lay public well aware of environmental problems (“Minimata” and “iati-iati” diseases).

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Furthermore, inhalation of Pb, As, Hg and Cd compounds can be 3 to 10,000 times more effective than ingestion in delivering a dose to the body.” Most data available about metals in MSW compost and precursor materials are regarding total metal present, rather than the specific valence states and compounds, termed speciation. Metabolic water along with that added for operations, under locally acidic conditions generated by parts of the composting process, may mobilize metals in materials, but these in turn can be precipitated by basic anions as less soluble salts (in the overall neutra! compost) or bound to recalcitrant organic matter. Metals are expected to increase in concentration as composting removes carbonaceous biodegradables. Only where anaerobic conditions persist can alkylation of Hg and As permit their mobilization as volatile methylated analogs. Thus, workers are likely to be exposed to metals in their higher (and usually less obnoxious) valence states, such as AS”, which is less toxic and not carcinogenic in comparison to As”‘. As a counter example, however, Cr”’ is carcinogenic but Cr”’ is not only not carcinogenic but also is a required element. These issues-speciation and consequent toxicity and bioavailability-have prompted empirical studies of the relationship of blood or serum levels of metals of animals and people with respect to local dust and soil residues. Although these metals are present in dusts and aerosols from MSW, sewage, sludge, compost, etc., studies’4,29of workers have not identified either body burdens or diseases caused by these metals as problematic. More attention has been devoted to metals affecting plant growth, contaminating food crops or becoming available for inhalation or ingestion by children. Indeed, exposure to metals as air pollutants from other sources or as normal dietary components may be more important than compost exposure,40 even for compost workers. The disposable nature of a wide variety of manufactured goods (especially electronics, packaging materials, and printed goods) clearly offers the opportunity to introduce a range of metals into MSW. Inorganic materials are taken up from soil by plants and naturally occur in food and yard wastes. The composting process eliminates a substantial part of the carbon matrix in which these have been located and thus concentrates the non-degradable elements and may change their chemical form. Local acidity and the presence of natural products of

fermentation such as acetic, oxalic, and citric acids from bacteria can solubilize metal containers and similar substances, and the oxidation by non-biologic processes can convert “tin cans” to ferric oxides (rust). Hydrous ferric oxides can bind various metals, and presence of iron added to sludges in phosphate control is attributed to reduced availability of several metals in sludge.’ Degradation of plant materials may form phenols, carboxylic acids and amino compounds with a high affinity for some of the metal ions. Some metal ions may precipitate as insoluble carbonates, hydroxides, phosphates, or sulfates, with the proportion present depending on local pH, Eh, and soluble cation and anion concentrations. Under microaerophilic or anaerobic conditions such as might occur in compost with inadequate mixing and over-saturation with water, some of the metals can be reduced (e.g., Hg*+-Hg’) or alkylated by microbial processes (Hg*+ -+CH,Hg + -+(CH&Hg; AsO, -+ -(CH,),As) to volatile compounds with different toxicities than the original elemental forms. At the same time SOi- may be reduced to the reactive sulfide form yielding metal sulfides with greatly reduced bioavailability of the metal ion. All of these interacting processes are grouped under the heading of “speciation” with respect to the valence state, extent of alkylation, and covalent or coordinate covalent bond formation between the aqueous solution and the organic and inorganic polymers. In any case the exact species of elements in compost may not reflect the original composition of MSW entering the composting process. The critical issue is that much of the knowledge about the fate, toxicity, and nutritional value of most inorganics is dependent upon studies using simplified systems where the total metal content is (presumably) approximately that of a single ion species added to test materials. The dynamics of speciation thus present a formidable challenge to predictive assessments. Often little is actually known about speciation of these metals within MSW compost because analytical methods and means of sample preparation are directed at simplifying matters: everything is extracted with strong acids (much stronger than the weak organic acids present in the soil or compost) and oxidized to the highest valence state. Any empirical observations about the impacts of a given compost in a given soil with a set of crop plants may thus be difficult to extrapolate to other situations. Nevertheless, the conventions in risk assessment have had to

Risk assessment

issues for MSW compost

be structured around “total” metal availability (usually assumed to be 100% unless studies consistently demonstrate otherwise). The foregoing problems are aggravated further by two other features of metal ion chemistry and toxicology-(l) the wide range (up to 1050)of association constants (solubility products, binding constants, coordination constants) between metal ions and anionic forms or ligands and (2) the extent to which metals interact biologically in additive, synergistic, and antagonistic ways. These issues are important in the microbial ecology of soils, where fungi battle bacteria and each other with metal-binding antibiotics. Methods for, say, cation exchange capacity or other characterizations of the soil/compost matrix inadequately characterize potential availability and toxicity, and details of metal-metal interactions are lacking for most cases. Specific issues about inorganics are often in the forefront of assessment. Because the repeated application of metal-containing composts to a given soil and concomitant loss of organic matter might well lead to a build-up of metals in that soil, concerns about long-term outcomes have arisen in Europe where MSW composting has had a long history.14 Empirical studies of sludges and composts added to agricultural soils, however, indicate that the receiving soil approaches compost levels as a limit in terms of plant uptake.35 The Alternative Pollutant Limit approach3 seems to rest partly on the assumption that additions of inorganics as compost would eventually be balanced by losses in a steady-state process, such that direct exposure to compost is equivalent to compost amended soil and thus a central feature of both occupational and consumer risk assessment. If the fraction of net metal loss (additions less losses due to crop harvesting, volatilization, leaching, etc.) is proportionately greater than the annual net loss of soil and soil organic matter (due to biodegradation and erosion), then the concentration of metal in the soil will continually decrease. Otherwise, it would be expected to build up. Lisk and colleagues4’-43 have raised questions about a number of these inorganic components in waste streams leading to composts. Asbestos was detected in about 213 of wastewater sludges (possibly due to Transiteo”) (asbestos/concrete) pipes)42 and in about 50% of composts with and without either MSW or sewage sludge.43 Because no effort has yet been made to ascertain

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sources or even bioavailabilities of asbestos as dusts or inclusions, such discoveries are difficult to differentiate from background exposures and may be meaningless in regard to the choice of waste management method. Finally, any assessment of the role of metals must recognize the geologic nature of the scale and extent of how life has evolved in relation to local, regional and global deficiencies and excesses of each element and in relation to each other over time and space. Tolerance to excess and resistance to deficiency have been acquired at all levels of biota. Human activities may stimulate or disrupt these relationships in many ways, but natural processes redistributing these elements have clearly been at work for eons and continue into the future. Understanding whether anthropogenic activities threaten the natural processes ultimately is at the heart of the risk assessment process. 3.6. Allergens Allergens are lipopolysaccharides or proteins liberated by the breakdown of microbes, microinvertebrates, or the vegetable matter on which they are growing. As dusts to be inhaled or to enter open cuts or sores in the skin, these materials can evoke local inflammation and congestion or precipitate a full blown immunologic response of serious proportions in sensitive individuals. Such sensitization appears to be overcome by repeated, chronic exposure, such that workers develop resistance to this response over time. There is little information’* on the number of workers leaving employment in MSW-related occupations because of allergic reaction, but it appears to be a factor similar to odors, in which some self-selection limits worker complaints and loss-of-time disability. 3.7. Other materials Although detailed, broad studies are not available. workers are clearly at risk from the corrosive, explosive, and flammable nature of unprocessed wastes in MSW. “Sharps’‘-the broken glass, metal edges, etc.-require physical protection. These present chronic problems for which management, training, and process equipment design are a needed and proven response.‘5 4. EXPOSURE

ASSESSMENT

Almost all worker exposure to infective and toxic materials in MSW and compost originates

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as dusts, aerosols and vapors, but will include ingestion and dermal routes as well as inhalation. Particulate/aerosol size determines the extent to which inhaled material is retained in the lung or intercepted in the upper respiratory tract and either expectorated or ingested, the extent to which air-borne contaminants are deposited on skin or clothing to provide opportunities for dermal uptake or ingestion, and the extent to which the process serves as a source of off-site contamination. Metal salt dusts and certain microbes (e.g., Pseudomonas svringae, P. erwinia, Klebsiella spp.) act as nucleation agents in creating aerosols within humid air of closed facilities. Any process equipment breaking up the MSW (e.g., hammer mills, shredders) clearly would be a major source, as Clark et aLI discovered in their study of Swedish MSW composting facilities regarding micro-organisms, endotoxins and dusts. The mere presence of toxicants, pathogens and allergens does not necessarily create a risky situation, even when a set of exposure pathways can be demonstrated; for pathogens there must be a minimal dose or infective unit of the organisms, and chemicals must be bioavailable and absorbed into the body at levels greater than any threshold dosage, if such exist. Both of these factors are significant features of the exposure to MSW compost dusts. In theory, it should be possible to estimate the risk of infection by determining both the minimal number of organisms (“infective unit”) required to produce an infection in a vulnerable individual and the number of infective units available in a unit of MSW or MSW compost over a given time period. Unfortunately, the technology for quantitative determination of infective units or any equivalent is often lacking or suspect;13 moreover, sampling feedstocks containing such diversity (as does MSW”) is difficult for any particular item. In the case of pathogens mixed into a diverse matrix, such a problem is magnified. Pahren# reviewed the limited number of applicable studies and noted the technical difficulty in just the sampling process itself, since the air stream of typical samplers could desiccate organisms on the filter and high volume samplers must be used. On the other hand, Clark et ~1.‘~ found that dust levels of 0.14-10.6mg mm3 contained up to 10’ colony forming units (CFUs) of gram-negative bacteria, > IO6 CFU of A. fumigatus, and l-42 ng of endotoxin per m3. Armstrong and Peterson4s

reported values as high as 252 CFU mm3 in the processing building and 152 CFU m--3 outside. In an MSW recovery facility Lembke and Knisely 46 found IO5 CFU me3 inside and lo4 CFU rnmm3 at the landfill. A more detailed study by Mansdorf et aL4’ covering a wide range of facility types, reported total organisms at 103-10’ CFU rnm3, but only A. fumigatus and Streptomyces spp. at 2 104mm3. Most gramnegatives were I lo3 mm3 or undetectable, and viruses present in MSW could not be found in aerosols. Epstein and Epstein26 reported A. fumigutus at 110-120 CFU me3 at a compost site in Ontario, where background levels were about 2 CFU rne3. Estimates of particle size designate the deep respirable fraction at 30%” and the total respirable fraction at 47-90%.” No information is available about the composition of MSW particulates with respect to size distribution, so an assumption is generally made that they are randomly derived from the MSW and compost. Given the extreme variety of MSW handling, source control, sorting, and commutation practices in composting operations, this assumption leaves much room for questions, but Lisk et ~21.~’found much less variability in MSW composts and feedstocks than expected from the diverse origins. The report by Vogt and Walsh48 of the importance of paper as a carrier of coliforms and streptococci and the contribution of paper to “fines” imply that information on particulate composition is necessary for exposure assessment. 4. I. Key pathways/targets The means and forms by which a chemical moves from a source to a target where it might have an effect is termed an “exposure pathway”. Detailed knowledge of the pathway49 permits estimation of the rate and duration of exposure of the target to the parent material and its breakdown products or metabolites. The sum of the several pathways based on detailed conditions and attendant assumptions constitutes the “exposure scenario” used by the risk assessor. Examination of these pathways can also lead to early determination of risk management options yielding the greatest reductions in risk. Occupational exposures, primarily via dermal and inhalation routes, are often the easiest to describe. Physical details of the workplace and its operations form the backdrop to advective movement of chemicals or other stressants from a relatively well-defined source to the worker whose time-motion in relation to the source and

Risk assessment issues for MSW compost

pathways(s) can, be monitored by a variety of means. Amounts of the same or similar agents workers may be exposed to outside of the workplace are often unknown. The exposure via a particular pathway may vary over the three composting stages (initial introduction and sorting, early handling of moist cornposting materials, and handling of relatively dry finished compost). Pathways of exposure of workers using composted MSW in agriculture, horticulture and landscape remediation (e.g., strip mine reclamation or Superfund site capping) may differ somewhat from those to which the general public might be exposed via residential use of compost or dietary uptake from crops grown on MSW compost. Structurally, however, residential pathways are largely extensions of the above or differ principally in terms of the extent and intensity of exposure. In the case of a child’s ingestion of soil, the pathway may appear to be qualitatively different for residential exposure, although workers and others may ingest soil from their hands (eating, smoking) and by inhalation of dusts, which are trapped in cilia. Unrestricted use of MSW compost by home gardeners offers a set of fairly well understood exposures to the adults and children. Soil is assumed to approach the range of values in the compost itself as long-term usage of the compost dilutes out the mineral soils. Some exposure to dusts occurs during compost use (e.g., application and tillage), but most of those receiving residential exposure are assumed to ingest (1) the compost itself (pica by children, adventitious soil ingestion by children and adults), (2) vegetables grown in it, and (3) meat and milk produced from feed grown on it. Inhalation of soil as yard dust resuspended by activities or household dust from soil tracked indoors constitutes a second cluster of pathways. In addition, some scenarios have presumed that fish exposed to runoff from compost-treated fields would be part of the diet. Superficially, it would seem possible to have a simple pathway from compost-applied land to a waterway in which fish could bioaccumulate the lipophilic materials and heavy metals from the MSW compost, as was proposed by the U.S.E.P.A. in evaluating paper and pulp mill sludge compost.50 However, erosion is needed to deliver any significant quantity of amended soil to the water, and that implies a heavy rainfall and subsequent

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stream hydraulics resulting in deposition of the eroded soil as sediment in catchments and points of reduced stream velocity (reservoirs, flood plains, estuaries, etc.). The fish pathway could therefore not be a residential pathway per se,” but should be evaluated in a more general sense. Exposure pathways to non-human organisms require a specific scenario for realistic assessment. U.S.E.P.A.% examined agricultural, land reclamation and forest soil applications of paper and pulp sludge composts. Again, as for the residential pathways, compost-amended soil is assumed to become contaminated to the same levels as compost itself. Subsequently, this soil can then be ingested by soil invertebrates which may bioaccumulate some metals and persistent, lipophilic organics and pass them on to other invertebrates and vertebrates higher in the food web. These soils might be eroded and distributed to the flood plain or to embayments, estuaries and other points of sediment deposition.” From there, the movement of chemicals into the food web could continue to afford opportunities for bioaccumulation. As identified by U.S.E.P.A.M and as implied by the PCB food web mode15’ birds and mammals feeding on soil- and sediment-dwelling invertebrates would eventually mobilize persistent organics and metals to top-level carnivores of concern as endangered species (e.g., bald and gold eagles), economically valuable species (e.g., mink, salmon), or aesthetically important species (e.g., otter). 5. RISK CHARACTERIZATION

The risk characterization of any particular facility employed for the collection and composting of MSW is so highly dependent on the incoming materials, the equipment used in sorting, etc., and operational variables that a generic classification is impossible. Existing operations range from those with clear problems’4 to more benign situations’yJ6*27 in which exposures to pathogen- and endotoxin-containing dusts are present, but insufficient to elicit immune response or disease. Indeed, the limited occupational health studies of sewage and compost workers “~‘y,2y do not find these workers to be particularly at risk from toxic or microbiologic threats, although adverse working conditions (dust, odor, etc.) and injuries were negative features. The presence of carcinogens, other developmental toxicants and heavy metals in the dusts

J.

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of MSW handling facilities present both noncarcinogenic and carcinogenic risks. In terms of assessments, the non-carcinogenic materials are presumed to have a threshold or exposure level below which no adverse effect occurs. The implications of genotoxicity of various viruses and the promotional effects of heavy microbial exposure also need to be considered. 5.1. PPLV

method

Rosenblatt et al.‘* introduced the concept of generic limits to exposure via designated pathways by a process-PPLV (Priority Pollutant Limit Value)-intended to indicate the potential clean-up requirements at Department of Defense hazardous waste sites undergoing remediation where the potential land uses were known or, alternatively, to indicate the limits to use if the available remediation technologies can achieve only a given level of pollutant removal. In residential occupancy, for example, with possibilities of home gardens, consumption of contaminated soil by children, and air-borne and tracked-in dusts entering the homes, backcalculation through the transfer and uptake efficiency from allowable daily exposure limits can estimate the PPLV contributed from several sources through multiple pathways and allocate these contributions proportionately. Fordham and Reagani redirected the emphasis of this approach more broadly to environmental concerns and introduced the use of environmental loss terms (to account for biodegradation during transfers). As a part of the evaluation effort at the Rocky Mountain Arsenal Superfund site the foregoing established the ease with which a very large number of chemicals might be organized into a manageable database including multiple sources and pathways therefrom to potentially valuable and vulnerable targets. Although the model of Fordham and Reagan53 is based on hypothetical or constructed food chains of “representative” species without established links among themselves or to other wildlife, other studies” imply that their model formulation may be adequate to the level of data availability and overall uncertainty. The key issues in this approach are (1) use of surrogate relationships and species-specific data to estimate flux from media to selected species including human beings, (2) presumption of bioavailability with respect to “total” measured pollutant and irrespective of metal species, for example, (3) presumption of suitable numbers of these representative species to effectuate the

assumed movement, and (4) additivity of outcome and hence exposure with respect to any given endpoint. Some problems are circumvented by relying extensively on whatever empirical, site-specific, or local data on bioavailability and transfer might be at hand. The Ram model” uses about every piece of available information on the extant food web in the Lake Erie/Ontario/St. Lawrence River bioregion,54 but still falls far short of a complete and definitive representation of the entire food web. For example, although it can cluster likefeeding species (i.e., those using the same species or group of species for food) and thereby represent species on which there is little speciesspecific information, it depends upon historically derived data on food web relationships which may have been altered by pollutants and natural and anthropogenic activities. Nevertheless, this food web guild model has successfully represented PCB distributions in about 260 species for which there are data on about 45 spp. This model would support development of criteria for “representativeness” using the approach of Fordham and Reagan.s3 5.2. Alternative

pollutant

limit

(APL)

method

Chaney55 opined that composts, sludges and similar materials might be applied to land used for crops, residences, etc., without restriction if the no-observed-adverse-effect-level (NOAEL) of individual constituents in the material with respect to the most sensitive response was not attained for the “Most Exposed Individual” (MEI). As with the PPLV approach, pathways of exposure are designated and the exposure concentration calculated as that not expected to exceed a specified level of effect. In Chaney et a1.9 and elsewhere this approach employs an outcome of 1Om4(1 cancer in 10,000 people exposed at the specified level for a 70-year lifetime) instead of the more generally accepted 10 ~6 de minimis level. Because this approach is designed to be applied largely to the processed product as “distributed and marketed” (D&M) sludge or compost, a set of “conservative” assumptions are employed. However, pathways are not summed for a given pollutant nor are exposures to equivalently acting agents combined. These calculations are compared to observed outcomes of animal exposures to treated pastures, feed from treated land, etc., in contrast to data about effects of toxicants added to sludge or compost, and thus emphasizes bioavailability and realism of transfer rates.

Risk assessment

issues for MSW compost

Low bioavailability of metals from sludges (especially those amended with hydrated ferric oxides in phosphate removal) and most MSW composts in which “green” wastes predominate appears to be a major factor in the suitability of MSW compost or compost prepared by cocornposting MSW with wastewater sludge.s6 The role of source separation” and even the extent to which metals management now obviates adventitious contamination are factors in the trends now being noticed regarding calculated health risks and observed phytotoxicity, for example, in MSW composts5 5.3. Uncertainty analysis Finkel’ characterized the uncertainty with which outcomes of environmental assessments are expressed. Indeed, the whole risk assessment process is an exercise engendered by the need to make decisions under uncertainty. In addition to the decision uncertainty (policy uncertainties, about which we can do little), uncertainties arise from processes within the system (stochastic and biologic uncertainties), within instrumentation and data collection (data collection uncertainties), and with systems of data management (modelling uncertainties). These last three sets of uncertainties can be limited by research. Stochastic uncertainties can be mapped as distributions with respect to important factors (e.g., the probability distributions of air temperature at a given point on the earth’s surface at any instant in time; the distribution of important genes in a target population and the phenotypic expression thereof in a community). Data collection and measurement can be standardized and subjected to a variety of practices under a quality assurance/quality control (QA/QC) program or Good Laboratory Practices program; the collection itself can be organized to attain accuracy, precision, relevance, completeness, and comprehensiveness. The statistical and other data management models can be compared against alternative hypotheses. assumption, and model structures. Exactly how these three sets of uncertainties are understood and presented to the risk manager therefore becomes a critical part of the overall decision-making process.’ Traditionally, scientific data are presented as having statistical variation, and many will accept that as the expression of uncertainty. Mean values of parameters and limiting sets of assumptions are used to provide a point estimate which can be compared to some

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“bright line” standard. Investigators may OCcasionally take this a step or two further, by examining the sensitivity of outputs to discrete changes in model parameters (sensitivity analysis) or structure. Unfortunately, the system of sensitivity analysis (including its semantic issues) does little good if the risk manager does not fully comprehend the implications of that about which we are certain in contrast to that about which we know little.’ It would be much better if we could express the extent of our certitude about a decision or assessment rather than its negative counterpart. The state of affairs is such that presentation of all the factors causing risk to vary in, say, the production of MSW compost can overwhelm the decision maker. One approach to simplifying parts of the decision making process is to simulate the outcomes of many runs of risk assessment models using the complete range of available data characterized with respect to its variation in relation to as many parameters as are known to affect exposure and effect. This parameter variation can include the distribution with respect to stochastic and genetic factors. The histogram or frequency diagram of these simulations reveals the gamut of outcomes as best we can describe them. Any point selected as “critical” has above it the frequency with which it is exceeded, and comparison of that “excedence frequency” for alternative scenarios, model structures, and assessment endpoints is far more revealing of the problems facing the risk manager than a ratio of the mean point value to a “bright” line. The major reason for this view is that many risk factors, including residue distributions and other exposure features, are lognormally or non-linearly distributed in such a manner as to have a small, but highly exposed or vulnerable portion of the population at-risk but unappreciated or even unrecognized on the basis of average values, presumed normally distributed means, etc, above the “conservative” cutoff of the 95% confidence interval. For example. 1% of children may consume soil at 100 x that of the “average” or “median” child, and Native Americans living off the land may obtain 50% of their protein from fish and wildlife and thus have 50 x exposure from a Superfund site. As a result, a small group may bear a very significant fraction of the total risk accepted by society as “not unreasonable” with respect to an anthropogenic activity.

.I. W.GILLETT

15x

The complexities of MSW compost management make its assessment an ideal candidate for simulation of the certitude with which data are available regarding human health and environmental risks. Preliminary analyses3’ imply that much of the risk may be below de minimis concerns, and that waste stream composition, including co-composting additions from the industrial and wastewater sectors, is adequately described by qualitative features in source separation. On the other hand, the temporal and spatial variation of chemical analyses of MSW compost and component waste streams feeding into those products have only recently received adequate attention such that these distributions can be described and used in simulations. For quantitative cancer risk assessment, the pathways can be computed and summed as arranged presently. Because the APL method relies on more realistic values than the MEI method, it or another modified form of the PPLV is an appropriate starting point. Using a spreadsheet such as LOTUS 123’TM’(IBM clone) or EXCELcTM)(Macintosh), the respective spreadsheet add-on manager @ RISKcTM)or @ RISK for EXCELcTM’ (Palisade Corp., Newfield, NY) can be applied to generate either Monte Carlo or Latin Hypercube simulations of the spreadsheet computations. The results can be summed and analyzed statistically to infer exceedences. It should be possible to input ranges of waste stream pollutant concentrations and their variation over time along with ranges of biodegradation coefficients, etc., to estimate product contamination and hence user risk. For non-carcinogenic risks, a similar procedure could indicate the frequency with which a threshold concentration is exceeded within a given time interval or for which the sum of {time x exposure} exceeds a threshold. This latter approach would fit in well wherever a “no net degradation” standard base is applied, as well as for comparative or incremental purposes. 6. POLICY ISSUES RAISED

Assessment of public and occupational health and safety and environmental suitability of the MSW composting process has at least superficially been unable to demonstrate serious threats from the conversion of MSW to compost, but at the same time not cleared away concerns about chronic or long-term threats regarding metals and persistent organics. In

addition, as noted earlier, the assessment process and risk management resulting therefrom have not faced directly issues such as incremental vs. total health risk, compost as a disposal means vs. compost as a useful amendment, and assessment of heterogeneous items providing inconstant, concurrent chemical exposure to mixtures. 6.1. Incremental vs. total risk Differences in the point of view of “risk” by diverse statues, agencies at the international, federal and state/local level, and scientific disciplines have largely resulted in a focus on incremental risk with respect to a particular With pesticides, the activity. regulated U.S.E.P.A. takes cognizance of total pesticide use for each nominal ingredient in its decision as to whether any additional uses should be registered. Under the Toxic Substances Control Act (TSCA), the U.S.E.P.A. must ascertain whether a “significant new use” alters an earlier decision not to enjoin the manufacture of a substance submitted for Pre-Manufacturing Notification review in terms of unreasonable exposure or hazard. The so-called harmonizing provisions of TSCA permit the agency to review other regulated inputs of a pollutant, although instances of oversight (dechlorane and KeponecTM)used as a truck tire flame retardant and insecticide, respectively) are readily cited. The potential widespread, unrestricted use of MSW compost produced with or without co-composting materials from sources responding to changing demands for waste minimization and product lifecycle scrutiny suggests that the ability to distinguish a direct, incremental input or exposure profile for a material/activity is becoming very diffuse. The more that MSW composting is accepted as a waste disposal option (in contrast to the somewhat more limited production of a useful soil amendment, v.i.), the more serious becomes the issue of whether total risk has been broadened excessively. A major issue in this regard, since a soil amendment for crops is at the heart of the matter, involves resolution of the exact meaning and limitations on the “Recommended Dietary Allowance” (RDA) of nutrient$’ and the “Reference Dose” (RfD) of the same chemicals as toxicants.j* These ranges (Table 1) can overlap or appear arbitrarily derived. RDAs are primarily based on studies of human beings consuming a varied diet adequate in terms of

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Table 1. Comparison of recommended daily allowances (RDA), reference doses (RfD), and drinking water standards for macro- and micro-nutrients Metal Fe Zn Se cu Mn F Cr”’ MO As, Ni, Si, Bb Cd, Pb. Li, Sn, V’ Cod

RDA’ kg kg-’ d-‘) SO@1000 25G833

1.7-2.5 40-100 60-100 1650 I .7-2.5 2.5-3.0

RfD’8 +g kg-’ d-‘) 200 3-3.5 40

5 (Cr”) 20 (Ni), 1(As) 1 (Cd), 0.32 (Pb)

Drinking watep olgl-‘) 300 5000 IO 1000 50 3000 50 (Cr”‘) 500 1000 (Ni), 50 (As) 10 (Cd), 100 (V”), 50 (Pb) 1000

“Ranges given generally reflect values within a range for &kg adult or 6-kg chiId.57 bEssentiality established for animals but not human beings. ‘Essentiality inferred for some animals but of dubious merit for human beings. dEssentiality as B,, the sole known or demonstrable requirement.

energy and presumed to have nutrients in an available form. These contrast with predictive toxicology studies which are often based on extrapolations from non-primate species fed purified or semi-purified diets to which the putative toxicant has been added, often without regard to form, speciation, or realism. This issue is part of the resolution necessary to consider ME1 vs. APL methods, for example. The most serious total exposure issue is that surrounding Pb and its dissipation following major reductions in inputs via batteries and leaded fuels. Even a small increment or remobilization may be very unsatisfactory for children in certain localities, but not others. Understanding of the importance of the timing and intensity of exposure relative to development and longterm consequences has been critical to creation of an improved risk management approach. Some MSW composts may contribute excessively to total Pb exposure. Bioavailability studies”T6’ are helpful in demonstrating the complexities of Pb release and uptake, but underscore the specific nature of the Pb-containing material as critical in determining outcomes. Moreover, the generic issue of total vs. incremental exposure needs resolution. 6.2. Recycling within compost use The view of MSW compost as a non-threatening and useful product of MSW disposal evokes conflicts between “risks” and “utilities” and has much to do with risk management decisions. Is MSW compost a diluent for possibly useful, but proscribed wastes (e.g., chrome tanning sludges rich in protein as well as Cr)? Can MSW compost quality be maintained even

if greengrocer wastes, etc., are diverted to alcohol production or other recycling efforts? With a broad and strong commitment to waste minimization and to avoidance of gratuitous use of industrial chemicals, the MSW waste stream itself is becoming less “toxic”. Does this assure that risks from MSW are becoming moot or at least will be within a few years? These types of questions reflect the dynamic nature of the source materials, their evaluation, and the product(s) and its (their) evaluation for utility and safety. Some states and federal governments have already addressed this question, but largely as if it were a fixed proposition with known hazards, exposure, and means of tying them together with vulnerable and valuable targets. Sequences of amendment of the composting stream with other wastes (sludge, flyash, and building materials, to name a few of the items which might provide bulk, nutrient and/or toxicants to the product) with respect to persistence, transformation, speciation, and bioavailability would appear to need much more extensive research and test method criteria development. Although some parts of society would like activities and products to be risk-free, the economics of risk management also make it clear that choices of the use of capital and operational funds in these ventures will require cost-benefit and cost-effectiveness comparisons.” 6.3. Multi-component interactions MSW is undoubtedly the worst case of multiple chemical exposure, because the waste stream potentially involves so much of products used by all levels and elements of society.

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Although there is some knowledge of the consequences of joint exposure to compounds within the same class being additive or non-interacting, we are already aware of interactions between persistent organics (e.g., PAHs and chlorinated aromatic chemicals). Exposures of production workers will be radically different from that of those using the MSW compost or products (food, land, etc.) which are exposed to it. A number of the VOCs with known or suspected neurotoxicity (e.g., hexane, ethyl benzene, acrylamide) are readily metabolized away in the course of compost formation, so that they would not be there to interact with persistent materials (chlorinated aromatic hydrocarbons, aryl phosphates, etc.). Induction of liver, kidney, intestinal and lung enzymes metabolizing many foreign chemicals is fairly well understood as not being “risk neutral,” since chemicals may be activated to toxicants as well as detoxified and one of the effects is to increase cell proliferation, thus enhancing promotion of carcinogenic lesions. For the most part, induction appears to have a no-effect dietary level of about 1 mg kg-’ (dietary toxicant concentration) for chlorinated aromatic hydrocarbons in rats, but the specificity and response of the AH-receptor for 2,3,7,%tetrachlorodibenzodioxin (TCDD) is linear over a range extending from > 1 pg kg-‘. “Dioxins” (TCDD and related polychlorinated dibenzodioxins and dibenzofurans) reacting with this receptor are likely to be sensitive effecters of interaction. 7. CONCLUSIONS

The assessment of risks to the environment, workers, and consumers presented by MSW compost has a number of unsettled issues. Serious, immediate and wide-spread threats are not evident, so most of these issues focus on long-term, chronic exposures and operational patterns within the composting and waste management industry. There clearly are components in MSW compost-persistent organics, metals, volatile organics and microbial/fungal toxins-which can cause harm from exposures at or somewhat higher than available through some exposure scenarios. Simulation analysis coupled with better studies of bioavailability of toxicants from MSW compost will help define the certainty of those risks. Removal of some of the uncertainties in this assessment process from the technical side, however, must be

accompanied by clear, insightful policies in risk management in its broadest sense. Thus, federal and state agencies must agree on the nature of the assessment processes to be employed for worker, consumer and environmental safety, identify operable risk goals, and then translate those goals into standards and related technical expressions for the risk assessor to use. Often, unrealistic expectations of one area of human activity can obscure serious risks from another quarter, and that frequently has been the recent experience with a wide range of issues in waste management. In particular, we need to assure ourselves and the workers involved that we are not jumping from the frying pan into the fire. It may be some time before agreement supports a full quantitative, multi-component risk assessment for MSW over the range of materials likely to be present. Research is urgently needed to flesh out concepts in speciation and bioavailability for inorganics, and the generation and biodegradation of bioactive organics within and from compost and composting organisms requires similar attention. The Alternative Pollutant Limit method or similar derivative of the PPLV approach will assist in definition of problems if not establishing justifiable levels of contaminant in MSW compost for unregulated use. Technical questions regarding implications of multicomponent exposures, incremental vs. total exposure, and exposures to nutrients and toxicants with overlapping ranges of effectiveness require urgent research. Environmental management is often pictured as a pendulum swinging first to a side of overcontrol and then to a side of over-indulgence and negligence. Citizens and officials attempting to deal with waste management at the local level not infrequently speak of being jerked around by higher authorities, including the electorate. The chaos of a double pendulum is mathematically understandable, but chaos within waste management costs everyone time and dollars. Composting of municipal solid wastes appears to be a means of simplifying and consolidating a number of waste management operations and even for eliminating certain risks. Acknowledgements-This work was supported in part by CKS Associates of Rochester, NY, and the Waste Management Institute of the Center for the Environment at Co&&l University. I am indebted to Mr. Steve Ebbs for his active participaiion and to Peter Woodbury, Tom Richard, and Ellen Harrison for useful discussions.

Risk assessment issues for MSW compost REFERENCES 1. D. E. C. 6 NYCRR Part 360, Solid Waste Management Facilities. Title 6 of the Official Compilation of Codes,

Rules and Regulations. New York State Department of Environmental Conservation, Division of Solid Waste. Albany, NY (1988). 2. S. Jasanoff, The Fifth Branch: Science Advisors as Policymakers. Harvard University Press, Cambridge, MA, 302 pp. (1990). 3. U.S.E.P.A., Development of Risk Assessment Methodology for Land Application of and Distribution and Marketing of Municipal Sludge. EPA/600/6-89/001.

U.S. Environmental Protection Agency, Washington, DC (1989). 4. L. W. Jacobs, A. C. Chang, R. L. Chaney, C. Frink, R. Horvath and J. A. Ryan, Distribution and marketing. W- 110 Peer Review Committee Analysis of the Proposed 503 Rule on Sewage Sludge (A. L. Page. T. J. Logan and

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