摘要:

This article reviews some of the current guidance concerning the separation of variability and uncertainty in presenting the results of human health and ecological risk assessments. Such guidance and some of the published examples of its implementation using two-stage Monte Carlo simulation methods have not emphasized the fact that there is considerable judgment involved in determining which input parameters can be modeled as purely variable or purely uncertain, and which require explicit treatment in both dimensions. Failure to discuss these choices leads to confusion and misunderstanding of the proposed methods. We conclude with an example illustrating some of the reasoning and statistical calculations that might be used to inform such choices.

ISSN:1080-7039    

DOI:10.1080/10807030091124419

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

摘要:

Effects of environmental stressors such as contaminants on the health of aquatic ecosystems usually involve a series of biological responses ranging from the biomolecular/biochemical to the population and community levels. To establish relationships and to determine the feasibility of extrapolating between higher and lower levels of biological organization, spatial patterns in fish responses to contaminant loading were investigated in a stream receiving point-source discharges of various contaminants near its headwaters. Relationships among fish responses at four major levels of biological organization (biochemical/physiological, individual, population, and community levels) were evaluated relative to patterns in contaminant loading along the spatial gradient of the stream. Both individual and integrated response analysis demonstrated that bioindicators at several levels of biological organization displayed similar downstream patterns in their response to contaminant loading within the stream. Some of the bioindicator responses at lower levels of organization appear to be useful for the ecological risk assessment process because of their sensitivity and apparent relationships to higher levels. By identifying and establishing relationships between levels of biological organization we should be better able to understand the mechanisms of stress responses in ecological systems that could ultimately result in improved predictive capability of ecological risk assessment and also allow for more informed decisions regarding remedial actions.

ISSN:1080-7039    

DOI:10.1080/10807030091124428

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

摘要:

As high trophic level organisms in the marine environment, fish-eating seals, dolphins and whales are often exposed to very high levels of fat-soluble environmental contaminants. Assessing the sources, levels and patterns of contaminants found in the tissues of marine mammals, and the biological effects of these contaminants on individuals, is essential to determining any population- or species-level impacts. While the number of contaminants to which marine mammals are exposed is staggering, designing strategies to assess the effects of complex mixtures represent a challenging yet vital part of an understanding of the “real world”. At present, an accumulated “weight of evidence” suggests that ambient levels of lipophilic contaminants have adversely affected aspects of reproduction, immune function and endocrine function in marine mammals inhabiting a number of industrial coastal regions. This body of evidence is drawn from a combination of (1) epidemiological or descriptive studies of effects observed in free-ranging populations of marine mammals inhabiting contaminated areas; (2) mechanistic, cause-and-effect, laboratory rodent studies, using single- or multiple- chemical exposures in acute or chronic designs; (3) semi-field or captive studies of marine mammals fed fish from contaminated areas; and (4) laboratory studies where rodent species are used as surrogates for marine mammals, and are exposed to extracts of complex contaminant mixtures found in fish. While these approaches have been used to delineate the effects of historically introduced environmental contaminants such as PCBs and DDT on wildlife, they may serve to identify the ecological risks presented by (1) the continued leaking of stored, discontinued, chemical supplies that have not yet been destroyed (e.g., PCBs); (2) new chemicals that may have lipophilic or persistent characteristics similar to those found currently in marine mammals; and (3) diet selection as a source of contaminants for humans, since certain human groups share the same food chain with marine mammals. Contaminant mixtures to which marine mammals are exposed differ greatly from the original industrial mixtures as a result of differing rates of accumulation and capacities to metabolize certain chemical types by the various trophic levels (e.g., invertebrates, fish, and marine mammals) of the food chain. Marine mammals ultimately provide information on the chemicals which present the greatest risk to consumers at the top of the food chain, something that cannot be adequately described or predicted in laboratory models.

ISSN:1080-7039    

DOI:10.1080/10807030091124437

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

摘要:

The Agricultural Health Study (AHS) has approximately 90,000 pesticide applicators and their spouses enrolled in a number of studies to determine whether exposures to specific pesticides are associated with various cancers and other adverse health outcomes. Although the AHS was intended to be an integrated program of studies, some significant difficulties have emerged. In this report, we examine the design of the AHS, identify important program strengths and flaws, suggest various improvements in the program, and recommend ancillary studies that could be undertaken to strengthen the AHS.Overall, the AHS is collecting a large amount of information on potential determinants of health status among farmers and farm families. A promising feature of the AHS is the prospective cohort study of cancers among farmers in which the research design determines exposures prior to the diagnosis of disease. More effort needs to be devoted to reducing selection bias and information bias. Success of the cohort study will depend in part on follow-up surveys of the cohort to determine how exposures and disease states change as the cohort ages. The cross-sectional and case-control studies planned in the AHS are less promising because they will be subject to some of the same criticisms, such as potentially biased and imprecise exposure assessment, that have characterized the existing literature in this field.Important limitations of the AHS include low and variable rates of subject response to administered surveys, concerns about the validity of some self-reported non-cancer health outcomes, limited understanding of the reliability and validity of self-reporting of chemical use, an insufficient program of biological monitoring to validate the exposure surrogates employed in the AHS questionnaires, possible confounding by unmeasured, nonchemical risk factors for disease, and the absence of detailed plans for data analysis and interpretation that include explicit, apriorihypotheses. Although the AHS is already well underway, most of these limitations can be addressed by the investigators if adequate resources are made available. If these limitations are not addressed, the large amounts of data generated in the AHS will be difficult to interpret. If the exposure and health data can be validated, the scientific value of the AHS should be substantial and enduring.A variety of research recommendations are made to strengthen the AHS. They include reliability and validity studies of farmer reporting of chemical use, biological monitoring studies of farmers and members of farm families, and validity studies of positive and negative self-reports of disease status. Both industry and government should consider expanded research programs to strengthen the AHS.

ISSN:1080-7039    

DOI:10.1080/10807030091124446

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

摘要:

Concern for both humans and wildlife has prompted regulatory agencies to search for methods to screen chemicals for disruption of regulation and responses to estrogen and other reproductive hormones. It is not clear whether tests suitable for hazard assessment in mammals also apply to oviparous (egg-laying) animals, or vice versa. Although estrogenic structures are similar across species, estrogen receptor (ER) differences affecting binding affinity and gene activation do occur. The primary function of estrogen in all species is control of ovulation; secondary functions are gender determination, development of secondary sex characteristics, regulation of mating and breeding behaviors, and regulation of calcium and water homeostasis. Major differences between mammals and egg-layers are production of the egg yolk protein vitellogenin by rrthe liver of oviparous species and eggshell formation. Methods for measuring estrogenic activity include production of gene products, cell proliferation assays, tissue responses, vitellogenin induction, hormone assays, egg production and fertility studies, and development of secondary sex characteristics. General cellular/subcellular tests are proposed for initial chemical screening; those that show estrogenic effects would be tested further using species-specificin vitroassays (e.g., relative binding affinity to the ER). Only those chemicals that elicit effects in this second tier, might need to be tested in a higher tier of whole organism studies.

ISSN:1080-7039    

DOI:10.1080/10807030091124455

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

摘要:

We investigate the uncertainties associated with modeling the potential health effects on piscivorous animals of mercury released to the atmosphere. The multimedia modeling system combines an atmospheric fate and transport model, an aquatic cycling model, and a terrestrial food web model. First, the modeling system is used to calculate point values of the animals' hazard quotients (i.e., measures of toxic dose). Next, we use a simplified version of the modeling system to conduct a probabilistic analysis for the Great Lakes region that takes into account input uncertainty, variability, and uncertainty and variability combined. The use of two different software packages for the combined uncertainty/variability analysis led to similar results except for high values (>90th percentile) where some differences were evident. A sensitivity study was performed on the combined uncertainty and variability analysis. Regional variability caused more than 70% of the variance in the results, with the fish bioaccumulation factor accounting for the majority of the variability. The major sources of uncertainty were the speciation of the mercury emissions, the lake pH, and the sediment burial rate.

ISSN:1080-7039    

DOI:10.1080/10807030091124464

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

摘要:

Environmental investigations of former industrial sites often detect the presence of chemicals for which no soil criteria exist and for which regulatory agencies have not derived estimates of toxic potency. This poses a considerable problem for making informed risk management decisions involving sites where such chemicals are present. As a result, a methodology has been developed for making risk-based decisions for chemicals of unknown toxic potency in soil at contaminated sites. The method is based on principles and procedures used by the US Food and Drug Administration (USFDA), the US Environmental Protection Agency (USEPA) and the Canadian Council of Ministers of the Environment (CCME). After analyzing the data on hundreds of carcinogenic and non-carcinogenic substances, the USFDA and other leading researchers have concluded that, if no toxicological data is available on a chemical, exposures less than 1.5 µg/person/day (i.e., 0.02 µg/kg body weight/day) are unlikely to result in appreciable health risks even if the substance was later found to be a carcinogen. To develop maximum soil concentrations that will be protective of human health (i.e., Risk Management Criteria or RMC), the above exposure limit of 0.02 µg/kg body weight/day has been assumed to be protective of risks from exposure to chemicals lacking toxicological data. Using a stochastic risk assessment model for estimating exposures to chemicals from contaminated sites, our analyses indicate that a soil concentration of 2 µg/g would be protective of human health for land uses that include residential, commercial, and industrial development provided no major indirect pathways exist at the site. If indirect pathways exists (e.g., vapor infiltration of soil gases, uptake of chemicals into garden produce, etc.), alternate RMC could be developed, that include such indirect pathways, using the methodology provided in this paper. Used by experienced risk assessors, the approach is a scientifically defensible screening method that will preclude many chemicals from unnecessary evaluation, while allowing risk assessors to focus efforts on chemicals of greater concern and make informed risk management decisions.

ISSN:1080-7039    

DOI:10.1080/10807030091124473

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

摘要:

The goal of this study was to conduct a probabilistic ecological risk assessment for tributyltin (TBT) in surface waters of the Chesapeake Bay watershed. Ecological risk was characterized by comparing the probability distributions of environmental exposure concentrations with the probability distributions of species response data determined from laboratory studies. The overlap of these distributions was a measure of risk to aquatic life. Tributyltin exposure data from the Chesapeake Bay watershed were available from over 3600 water column samples from 41 stations in nine basins from 1985 through 1996. Most of the stations were located in the Virginia waters of Chesapeake Bay, primarily the James, Elizabeth and York Rivers. In Maryland waters of the Bay, various marina, harbor and river systems were also sampled. As expected, the highest environmental concentrations of tributyltin (based on 90th percentiles) were reported in and near marina areas. The sources of TBT causing these high concentrations were primarily boat hulls and painting/depainting operations. Lower concentrations of TBT were reported in open water areas, such as the Potomac River, Choptank River and C and D Canal, where the density of boats was minimal. Temporal data from a ten year data base (1986-1996) from two areas in Virginia showed that TBT water column concentrations have declined since 1987 legislation prohibited the use of TBT paints on recreation boats (<25 m).Acute saltwater and freshwater TBT toxicity data were available for 43 and 23 species, respectively. Acute effects for saltwater species were reported for concentrations exceeding 420 ng/L; the lowest acute value for a freshwater species was 1110 ng/L. The acute 10th percentiles for all saltwater and freshwater species were 320 and 103 ng/L, respectively. The order of sensitivity from most to least sensitive for saltwater trophic groups and corresponding acute 10th percentiles were as follows: zooplankton (5 ng/L), phytoplankton (124 ng/L), benthos (312 ng/L) and fish (1009 ng/L). For freshwater species, the order of sensitivity from most to least sensitive trophic groups and corresponding acute 10th percentiles were: benthos (44 ng/L), zooplankton (400 ng/L), and fish (849 ng/L). Chronic data for both saltwater and freshwater species were limited to a few species in each water type. Based on these limited data, the saltwater and freshwater chronic 10th percentiles were 5 and 102 ng/L, respectively. Limited mesocosm and microcosm studies in saltwater suggested that TBT concentrations less than 50 ng/L did not impact the structure and function of biological communities.The saltwater acute (320 ng/L) and chronic (5 ng/L) 10th percentiles were used to determine ecological risk because all exposure data were from saltwater areas of the Chesapeake Bay watershed. Highest ecological risk was reported for marina areas in Maryland waters of Chesapeake Bay and for areas in Virginia such as the Elizabeth River, Hampton Creek and Sarah Creek. Low ecological risk was reported for areas such as the Potomac River, Choptank River, C and D Canal and Norfolk Harbor. Regulation of TBT on recreational watercraft in 1987 has successfully reduced water column concentrations of this organometallic compound. However, various studies have showed that TBT may remain in the sediment for years and continue to be source for water column exposures.

ISSN:1080-7039    

DOI:10.1080/10807030091124482

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

摘要:

Threshold tissue residue concentrations of polychlorinated biphenyls (PCBs) and 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs) were derived from the published results of semi-field (i.e., field collected food items were used as a medium of exposure to PCBs in laboratory reared animals) or field toxicity studies conducted with seals, European otters and mink. Based on biomagnification factors (BMFs) and concentrations of PCBs or TEQs measured in fish fed in the diet of experimental aquatic mammals, dietary threshold concentrations were estimated. Hepatic vitamin A, thyroid hormone concentration, suppression of natural killer (NK) cell activity and proliferative response of lymphocytes to mitogens were the toxicity endpoints measured in aquatic mammals. Threshold concentrations for PCBs or TEQs in livers of aquatic mammals to elicit the physiological effects ranged from 6.6 to 11 µg PCBs/g (geometric mean: 8.7 µ/g) and 160 to 1400 pg TEQs/g (geometric mean: 520 pg/g), lipid weight, respectively. The BMFs for PCBs and TEQs varied depending on the marine mammal species, and therefore the dietary threshold concentrations could be referred only by a range of values (rather than a mean value), which were 10 to 150 ng PCBs/g and 1.4 to 1.9 pg TEQs/g, wet weight, for PCBs and TEQs, respectively.

ISSN:1080-7039    

DOI:10.1080/10807030091124491

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor

ISSN:1080-7039    

DOI:10.1080/10807030091124509

出版商:TAYLOR & FRANCIS    

年代:2000

数据来源: Taylor