PHYTOTOXICITY STUDIES WITH LACTUCA-SATIVA IN SOIL AND NUTRIENT SOLUTION

The toxicity of 76 priority pollutants to lettuce (Lactuca sativa) was determined in soil and in nutrient solution. In the first case a static and in the latter a semistatic exposure was established. Volatile and easily degradable compounds had high EC50 values in soil (> 1,000 mug/g). In nutrient solution, however, several of these compounds were rather toxic. Quantitative structure activity relationships (QSARs) relating EC50 values to log K(ow) could be described for the toxicity in nutrient solution. Generally, the toxicity of the compounds increased with increasing lipophilicity. Deviations were (partly) caused by reactivity (N-containing compounds, double bonds in compounds), low lipophilicity (log K(ow) values < 1), and EC50 values close to solubility. To relate toxicity in soil and nutrient solution, soil EC50 values were recalculated to values in the soil pore water using calculated adsorption coefficients. Estimated pore-water EC50 values showed a good correlation with values determined in nutrient solution but were not equal to these values. The differences can be attributed to differences in exposure (static vs. semistatic).