|Toxicity Studies||Toxicity Tests|
|Uncertainty Factors||Future Needs|
The major questions in aquatic toxicology are:
(i) what combination of factors will minimize uncertainty of aquatic toxicity, and(ii) what additional studies should be done to validate that estimate of uncertainty.
"No instrument has been devised that will measure toxicity!"
instruments measure the concentrations of a toxicant.living material measures toxicity.
predict toxicity from measurements of both
- problems in environmental variations
- ie., physical, chemical and biological parameters
toxicity studies in aquatic environments
(1) time span
- toxicant may be rapidly degraded or transformed
- (chlorine and some detergents)
- =>short term toxicity test is sufficient
- except with chronic exposure (outfall)
- toxicant may be persistent and nondegradable
- DDT, PCB, elements
- long term toxicity test is needed(2) uncertainty(3) replicate conditions
- variation in environmental parameters
- pH, temperature, TSS, DOC, alkalinity,...
- batch tests => continuous flow tests
- standardize tests for monitoring programs
- do not standardize tests for research(4) test organisms
- original concept => most sensitive organisms
- current concept => most reliable predictor organisms
- current concept => most reliable predictor communities
- current concept => most reliable predictor ecosystems
- problems of keeping organisms alive for tests
- problems of keeping organisms in physiological state
- use common species for regulatory purposes(5) microcosms & mesocosms
- avoid concerns about testing higher organisms
- some evidence that test results with microorganisms are comparable to those with higher organisms
- microcosms & mesocosms are more environmentally complex
- better assay of environmental fate of toxicant(6) bioaccumulation
- persistent toxicants
- low solubility in water
- high solubility in fats & oils
"For the past century, our
philosophy has been that it is better to put waste anywhere (in air,
soil, groundwater) than into surface water such as streams and lakes. Although not openly
stated, our decisions bear out our policy. In view of the other emerging problems, that policy
must change, and, with it, aquatic toxicology."
Cairns, J. and D.I. Mount. 1990. Aquatic toxicology. Environmental Science and Technology 24: 154-161.