摘要:

Both performing and validating a detailed risk analysis of a complex system are costly and time-consuming undertakings. With the increased use of probabilistic risk analysis (PRA) in regulatory decision making, both regulated parties and regulators have generally favored the use of defaults, because they can greatly facilitate the process of performing a PRA in the first place, as well as the process of reviewing and verifying the PRA. The use of defaults may also ensure more uniform standards of PRA quality. However, regulatory agencies differ in their approaches to the use of default values, and the implications of these differences are not yet well understood. Moreover, large heterogeneity among licensees makes it difficult to set suitable defaults. This paper focuses on the effect of default values on estimates of risk. In particular, we explore the effects of different levels of conservatism in setting defaults, and their implications for the crafting of regulatory incentives. The results can help decision makers evaluate the levels of safety likely to result from their regulatory policies.

ISSN:1080-7039    

DOI:10.1080/10807039.1999.9657759

出版商:TAYLOR & FRANCIS    

年代:1999

数据来源: Taylor

摘要:

Over the last few years, many different types of sediment quality guidelines have been derived, and a debate has begun on how best to evaluate the predictive reliability of these guidelines. The reliability of sediment quality guidelines has important consequences for selection of specific guidelines for use, sampling designs, regulatory decision frameworks, and the extent to which biological testing is required to make decisions about dredging and cleanup actions. However, the authors of these studies are not all using the same terminology, the same definitions of errors and error rates, or the same methods of calculation. Definitions and general principles for determining the reliability of SQGs are proposed, to promote a common basis for discussion and comparison of the various SQGs available for use. Significant issues with current approaches to estimating reliability are also discussed.

ISSN:1080-7039    

DOI:10.1080/10807039.1999.9657760

出版商:TAYLOR & FRANCIS    

年代:1999

数据来源: Taylor

ISSN:1080-7039    

DOI:10.1080/10807039.1999.9657761

出版商:TAYLOR & FRANCIS    

年代:1999

数据来源: Taylor

摘要:

Until recently, parameters from microorganisms were generally not included in risk assessment at a comparable level to animals and plants. However, the major part of global biomass, biodiversity, and ecosystem processes is present in the microbial world and microbiological techniques applicable to risk assessment are becoming available. Two microbial indicators are described based on the usage of multiwell plates with different substrates and a redox indicator for monitoring mineralisation. With both techniques autochthonous microbial communities are analysed. Producing functional fingerprints of the microbial community gives insights into the composition of different functions. This is equivalent to observations of ecological abundance and species composition. When lack of reference sites or reference data renders risk assessment difficult, measurement of the pollution-induced community tolerance (PICT) can provide useful information.

ISSN:1080-7039    

DOI:10.1080/10807039.1999.9657730

出版商:TAYLOR & FRANCIS    

年代:1999

数据来源: Taylor

摘要:

The use of soil microorganisms in ecological risk assessment is hampered by an unclear dose-response relationship for most contaminants. Establishing dose-response curves for soil microbial communities requires that one have a clear estimate of exposure at the site of toxic action and a response free of confounding environmental factors. It is not clear what methods can estimate toxicant dose at the site of toxic action or determine microbial response to a toxicant. Pollution-induced community tolerance (PICT) is one possible estimate of microbial toxicant exposure. The PICT hypothesis is that the tolerance of a microbial community is proportional to thein situdose. This method automatically corrects for differences due to differences in soil physical-chemical variables between samples. Various components of the soil nitrogen cycle can act as microbial bioindicators of toxicant impacts. Estimating denitrifica-tion activity presents a number of advantages over other components of the nitrogen cycle. Denitrifying bacteria come from a diversity of habitats, can be autotrophic or heterotrophic, and denitrification is a well-defined enzymatic system, which allows the use of molecular tools. Determining denitrification may be a good estimate of effects of toxicants on microbial communities. However, given the state of our ignorance regarding soil microbial community structure and function, redundant estimates of exposure and effect are necessary to adequately characterize the response of microbial communities to toxicants.

ISSN:1080-7039    

DOI:10.1080/10807039.1999.9657731

出版商:TAYLOR & FRANCIS    

年代:1999

数据来源: Taylor

摘要:

Deleterious effects of heavy metals on soil microorganisms are reviewed in relation to the complexities involved in their study. There is strong evidence that soil microbes are more sensitive to heavy metals than animals or crop plants. Decisions concerning limits considered to be ‘safe’ in terms of protection of soil microorganisms or soil microbial processes from metal toxicity depend on the organisms considered and value judgements as to their importance. At present there is a large discrepancy in actual concentrations of heavy metals that are allowed to accumulate in agricultural soils between different countries. The approach of attempting to achieve zero accumulation of heavy metals in soils is undoubtedly the most conservative, but will severely restrict the recycling of sewage sludges to agricultural land.

ISSN:1080-7039    

DOI:10.1080/10807039.1999.9657732

出版商:TAYLOR & FRANCIS    

年代:1999

数据来源: Taylor

摘要:

The functional importance of bacteria and fungi in terrestrial systems is recognized widely. However, microbial population, community, and functional measurement endpoints change rapidly and across very short spatial scales. Measurement endpoints of microbes tend to be highly responsive to typical fluxes of temperature, moisture, oxygen, and many other noncontaminant factors. Functional redundancy across broad taxonomic groups enables wild swings in community composition without remarkable change in rates of decomposition or community respiration. Consequently, it is exceedingly difficult to relate specific microbial activities with indications of adverse and unacceptable environmental conditions. Moreover, changes in microbial processes do not necessarily result in consequences to plant and animal populations or communities, which in the end are the resources most commonly identified as those to be protected. Therefore, unless more definitive linkages are made between specific microbial effects and an adverse condition for typical assessment endpoint species, microbial endpoints will continue to have limited use in risk assessments; they will not drive the process as primary assessment endpoints.

ISSN:1080-7039    

DOI:10.1080/10807039.1999.9657733

出版商:TAYLOR & FRANCIS    

年代:1999

数据来源: Taylor

摘要:

Soil microorganisms are pivotal in ecological systems, it may not be possible to define an ecosystem where an impact on overall microorganism populations would not mean a severe impact on the ecosystem. They are as relevant to an ecosystem as any group of organisms could be. At the same time, it is very difficult to link impact on measurable microbial activities to ecological impacts. We lack the required understanding. The linkage fails because of: compensation processes—the ecological process is continued by organisms other than those measured; non-specific assays—the method used to measure activity may impose conditions that do not reflect ecological conditions and multiple and unknown interacting factors. Overall, the ambiguity in benefit/ detriment relationships for impacts on microbes is the largest problem. Here we describe several examples of successes and failures of soil microbial bioassays in applications related to soil cleanliness criteria and ecological risk assessment. The usefulness of the microbial bioassays remains in question.

ISSN:1080-7039    

DOI:10.1080/10807039.1999.9657734

出版商:TAYLOR & FRANCIS    

年代:1999

数据来源: Taylor

摘要:

In the past, ecological risk assessments (ERAs) have generally overlooked the soil microbial community when evaluating the impacts of contaminants in soil. However, the soil microbial community, which includes bacteria and fungi, performs functions necessary for overall ecosystem health, including nitrogen fixation, nutrient cycling, and even degradation of contaminants. The incorporation of the soil microbial community into ERA requires the compilation of adequate toxicity data to complete the hazard assessment phase of the risk assessment. A variety of soil microbial toxicity tests exist that provide rapid and inexpensive results. Surveys of the microbial community at a contaminated site may also provide insight as to their functioning in the presence of contaminants. This paper explores the use of toxicity tests and surveys to evaluate chemical toxicity to microbes. However, many questions related to the best methodological approach to an ERA of the soil microbial community have yet to be answered.

ISSN:1080-7039    

DOI:10.1080/10807039.1999.9657735

出版商:TAYLOR & FRANCIS    

年代:1999

数据来源: Taylor

摘要:

Soil microbial toxicity tests are seldom used in ecological risk assessments or in the development of regulatory criteria in the U.S. The primary reason is the lack of an explicit connection between these tests and assessment end-points. Soil microorganisms have three potential roles with respect to ecological assessment endpoints: properties of microbial communities may be end-points; microbial responses may be used to estimate effects on plant production; and microbial responses may be used as surrogates for responses of higher organisms. Rates of microbial processes are important to ecosystem function, and thus should be valued by regulatory agencies. However, the definition of the microbial assessment endpoint is often an impediment to its use in risk assessment. Decreases in rates are not always undesirable. Processes in a nutrient cycle are particularly difficult to define as endpoints, because what constitutes an adverse effect on a process is dependent on the rates of others. Microbial tests may be used as evidence in an assessment of plant production, but the dependence of plants on microbial processes is rarely considered. As assessment endpoints are better defined in the future, microbial ecologists and toxicologists should be provided with more direction for developing appropriate microbial tests.

ISSN:1080-7039    

DOI:10.1080/10807039.1999.9657736

出版商:TAYLOR & FRANCIS    

年代:1999

数据来源: Taylor