Field effects of simazine at lower trophic levels--a review.

Simazine is a triazine herbicide used in agriculture, pot-plant and tree production. The total concentrations (dissolved + adsorbed) in soil depend on the application rate, for example an application rate of 1500 g simazine/ha will result in approximately 4 mg simazine/kg in the top 1 cm. It may be spread to adjacent areas due to drift, runoff or evaporation. In fresh water concentrations approximately 4 microg simazine/l has been recorded. In aerial fallout--rain--concentrations of 0.680 microg simazine/l has been recorded. In both soil and water, degradation studies have in most cases shown DT50 times that vary between a few days and 150 days, indicating that total or near total disappearance time may be at least three times longer. Low temperatures and drought may prolong the dissipation time by a factor of two or more. Laboratory studies indicate that the primary site of decomposition in the aquatic environment is the sediment. Field studies showed deleterious effects of simazine on terrestrial invertebrates at application rates below 2 kg simazine/ha. The direct toxicity was not confirmed by laboratory results, however, these were sparse and did not cover a broad range of soil organisms. No field studies were found dealing with invertebrates, but laboratory studies have shown deleterious effects of simazine on aquatic invertebrates at concentrations above 20 microg simazine/l. Simazine is phytotoxic to many non-target species at rates below the recommended rate. At least under some environmental conditions, simazine can remain for a long time in the active layer and still be toxic to sensitive plants 1 year after application. Despite its phytotoxicity many plant species become more and more tolerant in cases of repeated use for many years and some have become resistant. Simazine is not highly toxic to soil microflora and algae, although some species definitely are affected both in an inhibitory and a stimulatory way. Most investigations predict no long-term consequences to soil and aquatic microflora in association with recommended and appropriate use giving rise to maximum expected environmental concentrations of 5 mg simazine/kg in soil and 4 microg simazine/l in water.