Challenges to tradition—Environmental toxicology in the 1980s

Abstract

The regulation of nearly all manufactured chemicals includes the close control of them from manufacture, transportation, and use to disposal with respect to effects on air, water, soil, and organisms by use of present U. S. laws. Monitoring data have set some examples of upper limits of concentrations occurring in these various media from chemicals having properties of persistence, bioconcentration, and large volume use. These concentrations for wildlife usually do not exceed 1 ppm in air, water, and soil, and are often parts per thousand or less levels. Based on laboratory and field data, and chemical and physical properties, the equilibrium and weather-directed distribution of concentrations of chemicals in various media can be calculated, predicted, or determined to help set the pattern of toxicological tests needed to match these environmental concentrations. These data are often accurate to within one order of magnitude. Rapid progress is being made in improving our ability to estimate such concentrations by modeling. EPA has proposed a list of tests and test methods which they “request” be used as the basis of preliminary decision making for hazard assessment of individual chemicals. Little flexibility is built into these tests which are pertinent to the particular chemical. Researchers have found surrogate organisms which are sensitive to many chemicals over a wide range of concentrations so that warning signals of toxicity problems can be identified at an early stage of the development and use of a chemical, with a minimum of testing. Depending on the use and distribution of the chemical a number of the tests which are sought for by EPA may not even be necessary at this stage. It is apparent that in an attempt to obtain maximum uniformity of test conditions and results, requirements for elimination of variables and accompanying details often exceeds the need for reasonable accuracy for purposes of hazard assessment. Surrogate methods such as the use of short-life-cycle species like Daphnia are available for preliminary estimation of the chronic toxicity of chemicals without performing time-consuming, expensive tests with fish. Test methods are available which more accurately reflect natural declines in food residues and modes and choice of intake of organisms than some currently recommended toxicity test methods. Ecosystem effects are the ultimate test in determining the effect of chemicals on the populations of organisms. However, ecosystem testing has so many naturally occurring variables and manmade nonchemical intrusions which affect populations that often the effect of chemicals is lost in the range of total variables occurring in the ecosystem. Effects on ecosystems are nebulous and difficult to describe, understand, or interpret. Until we know the extent and significance of natural changes in ecosystems it will be difficult to assess the effects of chemicals. The speed of recovery of any segment of a damaged ecosystem is another matter for consideration. Thus, at the current state of the art, ecosystem tests are not always illuminating or contributing to the determination of hazard. There is no efficient, economical way of testing all chemicals on any ecosystem, let alone all ecosystems. The principal problems of overlap of toxic concentrations with environmental concentrations appear to be in water. The role of sediments in controlling concentrations of chemicals in water or soil and their contributions to toxic effects are important. The presence of sediments usually results in decrease of acute exposure but sometimes in increased length of chronic exposure. Fish losses in the United States, while sometimes severe locally, are usually temporary and not complete, and populations are often quickly replaced. One of the principal problems with which the nation has to deal is the concept of no-effect concentrations of chemicals and how much loss of nontarget or even target organisms is acceptable. Humans have not learned to quantify losses from chemicals like they have from automobiles and many other everyday hazards such as alcohol and tobacco. It is the challenge of the 1980s to observe adverse effects of chemicals scientifically, place the facts into perspective, make value judgments suitable to both the public and the organisms in the environment, and control the use of chemicals which do not pass these judgments.