Design and Interpretation of Herbicide Anaerobic Aquatic Metabolism Studies

Herbicides may be exposed to a broad range of anaerobic conditions in the environment. This range can extend from weakly reducing conditions within typically aerobic compartments to stable, strongly reducing conditions in sites well removed from oxidative conditions. Currently, Federal Insecticide Fungicide and Rodenticide Act (FIFRA) regulatory guidelines specify the design criteria for guideline studies that frequently result in highly stable, strongly reducing test systems. These test systems do not simulate environments where herbicides are likely to occur. Design criteria for anaerobic aquatic test systems can influence the nature of the results of anaerobic aquatic metabolism studies as well as the relevance of these results to natural environmental processes. Design criteria which should be considered are the effects of sediment to water ratio, establishment of an anaerobic system, monitoring the reducing potential (Eh) of the system and the system Eh-pH relationship. These criteria influence how results are interpreted and the extrapolation of data to field environments where herbicides are likely to occur.

Cyst-Based Toxicity Tests. IV. The Potential of Ecotoxicological Tests for the Prediction of Acute Toxicity in Man as Evaluated on the First Ten Chemicals of the MEIC Programme

In the framework of the multicentre evaluation of in vitro cytotoxicity (MEIC) programme, the first ten chemicals of the prescribed list were tested for acute toxicity in four standardised cyst-based aquatic invertebrate tests, consisting of two rotifer species (the estuarine Brachionus plicatilis and the freshwater Brachionus calyciflorus) and two crustacean species (the halophilic anostracan Artemia salina and the freshwater anostracan Streptocephalus proboscideus). Mortality was the test criterion and toxic effects, expressed as 24-hour LC50 values, were correlated with rodent and human acute oral toxicity data. Generally, a good correlation was obtained between any of the invertebrate tests and the rodent data. Likewise, the predictive screening potential of the aquatic invertebrate tests for acute oral toxicity in man was slightly better than the rat test for eight (excluding diazepam and digoxin) and nine (including diazepam, excluding digoxin) of the ten substances. The aquatic test systems, however, appear to be more suitable for compounds soluble in water.

Variability of Test Systems Used to Assess Ecological Effects of Chemicals

Numerous chemicals may produce toxicological effects which are ecologically important. Assessment of risk to ecological systems from chemical exposures includes the use of biological test systems to evaluate toxicity. Most biological test systems are laboratory oriented with no clear environmental relevance. To help focus the selection of test systems, we developed a series of descriptions of test system characteristics and suggested some criteria for selecting test systems to determine ecological effect (Novak et al. 1985). Another step in selection process is this evaluation of the variability of aquatic test systems using published data. Using the relative standard deviation, v, we classify variability as Low (v < 10%), Medium (10% ≥ v< 20%), High (20% ≤ v ≤30%) and Very High (>30%).