GUIDELINES FOR EVALUATING SELENIUM DATA FROM AQUATIC MONITORING AND ASSESSMENT STUDIES

It is now possible to formulate diagnostic selenium concentrations in four distinct ecosystem-level components; water, food-chain, predatory fish (consuming fish or invertebrate prey), and aquatic birds. Waterb orne selenium concentrations of 2 mu g/1 or greater (parts per billion ; total recoverable basis in 0.45 mu filtered samples) should be consi dered hazardous to the health and long-term survival of fish and wildl ife populations due to the high potential for food-chain bioaccumulati on, dietary toxicity, and reproductive effects. In some cases, ultra-t race amounts of dissolved and particulate organic selenium may lead to bioaccumulation and toxicity even when total waterborne concentration s are less than 1 mu g/1. Food-chain organisms such as zooplankton, be nthic invertebrates, and certain forage fishes can accumulate up to 30 mu g/g dry weight selenium (some taxa up to 370 mu g/g) with no appar ent effect on survival or reproduction. However, the dietary toxicity threshold for fish and wildlife is only 3 mu g/g; these food organisms would supply a toxic dose of selenium while being unaffected themselv es. Because of this, food-chain organisms containing 3 mu g/g (parts p er million) dry weight or more should be viewed as potentially lethal to fish and aquatic birds that consume them. Biological effects thresh olds (dry weight) for the health and reproductive success of freshwate r and anadromous fish are: whole body = 4 mu g/g; skeletal muscle = 8 mu g/g; liver = 12 mu g/g; ovaries and eggs = 10 mu g/g. Effects thres holds for aquatic birds are: liver = 10 mu g/g; eggs = 3 mu g/g. The m ost precise way to evaluate potential reproductive impacts to adult fi sh and aquatic bird populations is to measure selenium concentrations in gravid ovaries and eggs. This single measure integrates waterborne and dietary exposure, and allows an evaluation based on the most sensi tive biological endpoint. Resource managers and aquatic biologists sho uld obtain measurements of selenium concentrations present in water, f ood-chain organisms, and fish and wildlife tissues in order to formula te a comprehensive and conclusive assessment of the overall selenium s tatus and health of aquatic ecosystems.