Sampling and Surveys
Although general sampling issues will have necessarily been addressed before the ERA reached the effects assessment stage, it is worthwhile to note a few of them here. This will ensure that the risk assessor has mentioned and considered the potential impacts of these issues. Field surveys and ambient media chemical analyses are also addressed.
Field Sampling
Before sample locations are determined, sampling “reaches” must be defined. These are areas that may be impacted by specific contaminant sources. For example, one stream may have several contaminant sources along its length; a reach may be defined as that area between two sources. Sampling in reaches allows for the determination of the relative contribution of various sources to observed toxicity. It is important not to forget to sample an appropriate background (or reference) site. In fact, it is better to have a few reference sites, to account for natural variability in the environment. In the past, there was a distinction between background (meaning pristine) and reference (meaning not impacted by this particular site). Since; however, the distinction is losing currency, it is necessary to know which definition is being used.
One facet of field sampling that is often forgotten when schedules are set is the problem of seasonality in field parameters. For a large portion of the country, winter hinders sampling efforts. For example, it is difficult to sample worms or fish when the ground and creeks are frozen. Also, bats hibernate during the winter, birds migrate, and rare plants are more difficult to identify when they are not in bloom. It is better to delay completion of a risk assessment than to collect data at an inappropriate time.
A waste site investigation will necessarily involve the coordination of a variety of investigators covering the various sampling tasks. The coordination is important in order to obtain results useful for the ERA. For example, whereas water concentrations may change dramatically over a short period of time, water samples being tested for toxicity should be taken at the same time and from the same location as those taken for chemical analysis. It is less critical to coordinate other activities, such as collection of sediment samples, since sediment concentrations take longer period to show contamination.
In ERA, samples of ambient media do not consist exclusively of groundwater, surface water, sediment, soil, and air; the biota must be included as well, to permit evaluation of contaminant exposure and effects. This important source of information, available to ecological risk assessors, may allow greater certainty in the ERA results.
Field Surveys
Field surveys have the advantage of giving a real‐world indication of effects. However, the cause of any observed effects is likely to be unknown. For example, a decrease in young of the year fish may be due to contaminants that impact fish eggs or larvae or may be due to natural causes, such as a storm event which caused increased water flow that eroded the spawning beds. Another disadvantage is that small changes are unlikely to be detected. Usually a greater than 20% decrease in a field parameter (e.g. population size, number of species) is necessary for deleterious change to be detected. Field surveys may be further complicated because without appropriate and comparable reference sites, interpretation of effects observed at the site is extremely difficult.
In the case of predictive ERAS, field surveys provide information on the environment that may receive contaminants in the future. It is important to have this information in order to document any future adverse impacts. Surveys may include threatened and endangered species surveys, aquatic and terrestrial community surveys, and wetland survey. We mention the latter in passing before turning to a consideration of speciation.
In the United States, a wetland survey must be done for the site to identify and, if necessary, delineate wetlands. Note, it is easier (and less expensive) to identify than to delineate wetlands. It would only be necessary to delineate a wetland if remediation or other activities necessitated the destruction of all or part of the wetlands.
Speciation
Information on the speciation of the chemical in various media may be useful for contaminants, such as arsenic or chromium that have species with very different relative toxicities. Before the samples are sent for analysis, it must be ascertained whether the analytical method used will have detection limits below the regulatory concentrations of interest (e.g. ARAR) and the concentration that would produce an unacceptable risk, unless this is not technically or economically feasible. If these detection limits cannot be met, there will be added uncertainty in the risk assessment, because it will not be known whether these contaminants are present or not, and hence whether they constitute a risk.
Chemical concentrations in media at a site, along with the abundant single chemical toxicity data available in the literature, may be used to determine the specific causes of the impacts observed in the field surveys or toxicity tests, and define the sources of the contamination. These data are used in predictive ERAs to model effects of contaminant exposures. However, the measured concentrations may not be indicative of the bioavailable fraction (e.g. chemicals may be bound to soil particles and hence not be available for uptake by organisms).
Sources of Other Effects Information
Supplementary information that may be useful in the interpretation of ecological data includes an analysis of biomarkers. Biomarkers serve as sensitive indicators in individual organisms of exposure to contaminants or other sublethal stressors. They are typically physiological or biochemical responses, such as enzyme concentrations, genetic abnormalities, histopathological abnormalities or body burdens of contaminants. While biomarkers give an indication of exposure to stressors, they cannot yield information on the impacts of this exposure on individuals. This is because ERA is concerned primarily with the viability of organism populations, not physiological effects in a single fish or bird. However, some biomarkers are chemical‐specific, and hence may provide valuable information on the potential cause of observed toxic effects. For example, increased blood levels of the enzyme δ‐amino‐levulinic acid dehydratase indicates exposure to lead.
Additional Effects that Figure in Many ERAs
Global Warming
The atmosphere allows solar radiation from the sun to pass through without significant absorption of energy. Some of the solar radiation reaching the surface of the Earth is absorbed, heating the land and water. Infrared radiation is emitted from the Earth’s surface, but certain gases in the atmosphere absorb this infrared radiation, and redirect a portion back to the surface, thus warming the planet and making life, as we know it, possible. This process is often referred to as the greenhouse effect. The surface temperature of the Earth will rise until a radiative equilibrium is achieved between the rate of solar radiation absorption and the rate of infrared radiation emission. Human activities, such as fossil‐fuel combustion, deforestation, agriculture, and large‐scale chemical production, have measurably altered the composition of gases in the atmosphere. Some believe that these alterations will lead to a warming of the Earth–atmosphere system by enhancement of the greenhouse effect.
The primary greenhouse gases (GHGs) are water vapor, carbon dioxide, methane, nitrous oxide, chlorofluorocarbons, and tropospheric (ground‐level) ozone. Water vapor is the most abundant GHG, but it is omitted because it is generally not from anthropogenic sources. Carbon dioxide contributes significantly to global warming due to its high emission rate and concentration. The major factors contributing to global warming potential of a chemical are infrared absorptive capacity and residence time in the atmosphere.
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