AQUATIC TOXICOLOGY

(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.

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

• physiologically different from humans
• questionable applicability of extrapolations
• =>subsequent monitoring (drugs & chemicals) in humans
• still, relatively simple (limited to mammalian species)

• extrapolations to an enormous number of species & taxonomic range
  • (e.g., from diatoms to whales)
• differences in size, physiology, life history, geographic region
• extrapolate from a single species in a bottle to an ecosystem
• >9 million chemicals listed in the Chemical Abstracts Service's Registry of Chemicals
• ~ 76,000 chemicals are in daily use
• ~ 30 -50 million species

• application factors (fractions or numbers)
  • adopted to standard response thresholds (e.g., LC₅₀ or NOEL)
  • compensate for uncertainties
• natural systems are resilient
  • transform and/or sequester toxicants
  • ex. copper to sediments & selenium to atmosphere
• critical flows are set at worst case levels
  • maximize margin of safety

(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

• reduce with increasing analyses
• problems of cost & sample design
• Figure 1
• Figures 2 & 3

(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

• interactions between ecotoxicologists and ecologists
  • develop & evaluate predictive models
• determine information redundancy
  • responses of different species & toxicants
• study toxic events (e.g., oil spills)
• develop global perspective
  • digesting organic wastes => CO₂ => green house effect
  • no open water discharges => groundwater injections & landfills