A need to know the condition of ecological resources at regional and national scales prompted the development of the EMAP probability-based survey to address questions regarding the extent of regional contamination. A probability sampling design was adopted because an entire population of streams or lakes would be too expensive to census. The only way to assure that the set of locations is selected without bias is to incorporate randomization into the selection process. Use of randomization also allows calculation of uncertainty in the estimates of condition that arise from the selection process. One important result of using probability sampling designs is that a snapshot of the condition of the entire resource can be obtained from the sample. The findings are often summarized as population statistics such as means, medians, variances, or proportions above or below some critical value.

Most aquatic ecotoxicologists believe that in order to manage aquatic ecosystems one must, with some level of confidence, know the biological status of the system to be managed. This is especially true if one of the management objectives is to maintain and/or restore the biological integrity of that system. One aspect of aquatic ecosystem management concerns the evaluation of chemical stressors in the system. The importance of biological endpoints in this aspect of management is captured by Cairns and Mount (1990): " No instrument has yet been devised that can measure toxicity! Chemical concentrations can be measured with an instrument but only living material can be used to measure toxicity." Aquatic ecologists and toxicologists believe that in order to adequately manage aquatic ecosystems, both the chemical, and biological status of the system needs to be measured. Ecotoxicologists understand that organisms respond to the totality of their environment and that simply defining that environment by measuring selected physical and chemical parameters is inadequate for two reasons. First, with chemical measures you only find what you are analyzing for, and second, even if all the chemical constituents could be measured, our understanding of the interactions of toxicants (additivity, synergism, antagonism, etc.) is simply inadequate to predict biological responses. In order to successfully design a monitoring approach for assessing the impact of pest control strategies on aquatic ecosystems there are five things that we need to be take into consideration, level of toxicity, duration of exposure, routes of exposure and scale.

The level of toxicity can be placed in four categories; 1) acute levels - short term level exposures measured in days, that result in lethal end points that are measured as LC50s or No Observable Acute Effect Levels (NOAELs); 2) chronic levels - longer term exposures measured in weeks or months that result in lethal, growth or reproductive impairment and measured as No Observable Effect Levels or Inhibition concentrations (IC50s or IC25s); 3) Bioaccumulative levels - low level long term exposures measured in months or years and reported as Bioconcentration Factors (BCFs); and 4) Carginogen levels - levels that are measured by anomalies in fish or cancer in humans that result from years to decades of exposure.

Duration of exposure is related to the concentrations that are present in the environment during all or some portion of the life cycle of aquatic organisms. For example, what is the concentration of a contaminant that is present in the spring during reproduction and egg hatching or insect emergence. It is important to know when, how long and at what concentration a pesticide is present in the aquatic environment. The routes of exposure of aquatic organisms are :the water column as soluble and/or absorbed concentrations; through the food chain and in the sediment as pore water and/or particles in the sediment. Sources if pesticides to the aquatic environment will be from the soil, runoff and wet/dry atmospheric deposition. Scale concerns are near field, area-wide, or regional. Near field exposures, might be lethal impacts associated just below a group of agricultural fields. Area-wide exposures can be within a watershed, while regional exposures are multi-watersheds or multi-state wide.

To assess the fate and effect of pesticides on receiving waters I propose that the EMAP probability design to select monitoring sites randomly and collect indicator information at these sites. The following indicators will be collected: surface water and sediment toxicity; water, sediment and fish tissue samples for pesticide analyses; bio-surveys for fish, macro-invertebrates, and periphyton, analyze microbial activity (sediment respiration and enzyme activity) and physical habitat measurements (in-stream and riparian zone measures). This information will be used to used to evaluate the levels of toxicity, duration of exposure, routes of exposure and biological resources that are or are not effected by pesticides.

Toxicity tests can be used to test short and long term effects of pesticides on water and sediments. The toxicity tests that can be used to test lethal and sublethal effects (impaired growth or reproduction) of pesticides on receiving waters and sediments are fathead minnows 48-hr or 7-day growth tests, Daphnia magna 96-hr survival and growth tests, duckweed 96-hr survival, growth and chlorophyl a inhibition test, and 7-day amphipod tests. Results of tests conducted with these organism are reported as percent water or sediment sample. For example, a water is collected from a site and split into two aliquotes. One is sent back to a lab for toxicity testing, the other for chemical analyses. The sample for toxicity testing is diluted with a standard laboratory water or site water from a reference site using some logarithmic series. LC50s, IC50s, and/or NOELs are calculated as percent sample. The concentrations of pesticides found in the sample that was saved and chemically analyzed are multiplied by these endpoints. For example, the LC50 of a water sample was found to be 25% and the concentration of atrazine was found to be 10 mg/l in the chemical samples analyzed. Therefore, the concentration of atrazine in the stream sample that is lethal to 50% of the test organisms is 0.25 X 10 = 2.5 mg/l. Some safety factor can be applied to this number so that a non-lethal goal for this pesticide can be set.

Safe concentrations determined in this way can be used with bio-assessments, microbial assays and physical habitat measurements to assess whether the aquatic communities are not impacted by pesticides within a watershed or larger area-wide region. Sites or watersheds that have no acute or chronic toxicity and diverse and taxa rich biological communities with good in-stream and riparian habitat can be used as control areas that can be used as standards or goals to compare other areas in a watershed or region where pest control practices are impacted in-stream biota.

Address:
U.S. Environmental Protection Agency
Ecosystems Research Branch
National Exposure Research Laboratory
26 W. Martin Luther King
Cincinnati, Ohio 45268

Phone: (513) 569 7076
Fax: (513) 569 7609
E-Mail: Lazorchak.Jim@EPA.Gov

Dr. Lazorchak is a Research Aquatic Ecologist and Toxicologist with the U.S. Environmental Protection Agency, National Exposure Research Laboratory in Ohio. He received his BS in Zoology from Southeast Missouri State University in 1969, his MS in Aquatic Ecology from Wright State University, Ohio in 1972, a second MS in Environmental Sciences from the University of Texas at Dallas in 1978 and his doctorate in Ecotoxicology from the University of Texas at Dallas in 1986.

His Current Activities are as the Research Aquatic Ecologist with the Ecosystems Research Branch in the Office of Research and Development, U.S. EPA. He is responsible for the design and coordination of logistics for the U.S. EPA Environmental Monitoring and Assessment Program (EMAP) a field monitoring program for lakes and streams. He is the indicator lead for research and assessment for fish contamination, water and sediment toxicity and the co-lead for zooplankton and macroinvertebrates. He is also the senior ecotoxicologist and manager of an Aquatic Research facility for ecotoxicity methods development and research. His latest research is in the area of real-time biological monitoring using clams and fish to detect episodic and long term exposures to contaminants.