Formulation of Water Quality Standards to Protect Aquatic Life
Water quality standards for aquatic life protection are required only for those chemicals which are likely to occur in harmful concentrations within the aquatic environment. The first requirement is to define the extent to which the aquatic ecosystem is to be protected; three broad categories which might be appropriate are described. The appropriate standard should be set on the basis of a 95 percentile compliance. This concentration might be greater than the NOEC for the most sensitive life stage of the most sensitive species, as measured by exposure to a constant concentration of the chemical under laboratory conditions. The standards should be firmly based on laboratory and field data, and be internally consistent. Some recent EPA standards have erred in this respect. Two general rules which apply to the validity of standards are outlined. Standards should take into account the effect of significant modifying variables such as water hardness and pH. The application of safety factors to the NOEC depends in part on the value of the resource to be protected. For those substances which are bioaccumulated to a significant extent, standards should be based on animal tissue concentration and not on aqueous concentration.