THE FACTOR TIME IN ASSESSING ECOTOXICITY:Studies with Herbicides and Metals applied singly and in combination to Lemna minor in simple and complex exposure patterns.

Ecotoxicological toxicity data serve as a basis to assess the hazard of a substance and help to decide whether a risk of adverse effects in the environment is likely. Toxicity tests are often restricted to simple single substance tests with short time periods of exposure. They only regard toxicity at a certain time point distinguishing only between acute or chronic toxicity. However, time consists of many timescales, like toxicodynamic, the dynamics of injury and recovery and toxicokinetic, the dynamics of absorption and elimination of a toxicant. Additionally, the exposure to hazardous compounds may not follow simple exposure patterns. Environmental concentrations of pollutants may fluctuate, due to variable emissions from anthropogenic sources such as the seasonal use of herbicides and storm runoff or flooding. As a result, organisms can be exposed to a multitude of different toxicants with complex time patterns. Taking these aspects into consideration, the aim of this study is to gain an insight into what influence time has on toxicity and how toxicity develops if the exposure follows complex time patterns.