Pesticides in limnic metabolism: a review on the application of nuclear techniques

Pesticides in fresh water ecosystems are discussed with respect to their toxicity, bioaccumulation, degradability and transportation. Water quality problems centre around the balance or imbalance between oxygen supply, primary production and community respiration. Sources of pesticides are runoff, leaching, adverse deposition of pesticides from agriculture and, in certain areas, industrial sources. Several bioassays for toxicity tests are described. For photoautotrophic activity (algae, particularly Scenedesmus quadricauda) growth is monitored by: turbidity, cell counting, chlorophyll determination, oxygen production or 14C incorporation; for heterotrophic activity: oxygen consumption, dehydrogenase activity, grazing capacity of protozoa, acidification by Pseudomonas, ATP, production of HTO or 14C-dioxide from 14C- or 3H-acetate or glucose; for higher animals: adverse behaviour or death. Radioenzymatic and radioimmunoassays have also been used. Often adverse effects, e.g. on fish (taste, poor health), are observed, but unequivocal causative relationships to particular pesticides or polluters can seldom be established. Metabolic transformations of pesticides in organisms are very involved; they include: oxidation, hydrolysis, reduction, conjugation, dehydrohalogenation, ring scission, hydration and chelation (metals). Some guidelines are established and experiments, particularly with 14C label, are reported. Bioaccumulation occurs mainly in fat and bone. Concentrations take place in the food chain. Research methods are similar to those for degradation. In water, pesticides may be transported as dissolved material or by adhering to suspended sediments. Some studies on isotopic and non-isotopic sediment tagging are reported. (author)