A chemostat system for investigating pesticide biodegradation in continuous mixed bacteria cultures originating from surface water.

To be able to predict the degradation (rate) of organic chemicals (e.g. pesticides) in the field, knowledge of the environmental conditions that are of influence on the degradation process are of importance. In the present study an experimental system is described which is used to study the degradation of organic pollutants in mixed bacteria cultures originating from surface water With this system the degradation of compounds can be followed for relatively long experimental periods (months). In addition, it is possible to vary different environmental parameters in order to investigate their influences on the degradation of the chemical. These preliminary experiments show that growth and 'composition' of the bacteria culture have comparable patterns in parallel experiments. The first order degradation rate constant for the test compound dichloran, as calculated from these experiments under these circumstances, is about 0.002 h(-1).

Relative risks of transformation products of pesticides for aquatic ecosystems.

In this study, the availability of physico-chemical and ecotoxicological information on 78 transformation products for 20 regularly used pesticides in the open literature is evaluated. Based on this information, it is attempted to predict the relative risk for the aquatic environment of each transformation product in comparison to its parent pesticide. It is concluded that for the 78 transformation products selected, the data set on physico-chemical and ecotoxicological behaviour is not very large. Measured log Kow values and other physico-chemical properties are known for only 30-40% of the selected transformation products. The overall reliability of the collected physico-chemical values is considered to be moderate to slight, while for the ecotoxicological data set, reliability is considered to be sufficient. In many cases, there is a need for more information especially on the persistency and no-observed-effect concentrations of the pesticide's transformation products. In general, over 50% of the transformation products of triazines, carbamates and phenoxypropionic acids pose, in theory, a similar to higher risk than their parent pesticide, while over 50% of the transformation products of synthetic pyrethroids, organophosporous pesticides and dithiocarbamates probably pose less risk. High risk was expected for products with high accumulation or persistency in sediment and/or high toxicity together with considerable bioaccumulation (potential) or relatively high concentrations or persistency in water. A generalization of the joint features that caused an increased risk for ecosystems could not be made for most pesticide classes. Exceptions are the synthetic pyrethroids, for which transformation products with a similar or even higher log Kow than the parent pesticide caused an increased potential risk, while for the carbamates the presence of the carbamate group in the transformation product was the joint characteristic of chemicals with predicted increased risk. For three transformation products, monitoring data based on concentrations measured in surface water in The Netherlands were compared with maximum permissible concentrations. This comparison indicated that two of these compounds pose a potential risk of adverse effects in the field situation in Dutch aquatic ecosystems. For all other transformation products, the potential risk in the field situation could not be established because of the absence of monitoring data.

Sorption kinetics of chlorinated hydrophobie organic chemicals : Part I: The Use Of First-Order Kinetic Multi-Compartment Models.

This is the first of a two-part series describing the Sorption kinetics of hydrophobic organic chemicals. This paper discusses the use of first-order kinetic compartment models in environmental studies, of subjects such as bioaccumulation and sorption. A comprehensive mathematical description and model calculations are presented. Differences between these models and the pharmacokinetic compartment models will be indicated, emphasis being given to the use of the former in sorption studies.

Sorption kinetics of chlorinated hydrophobic organic chemicals : Part II: Desorption experiments.

This is the second of a two-part series describing the sorption kinetics of hydrophobic organic chemicals. Part I "The Use of First-Order Kinetic Multi-Compartment Models" is published in issue 1 of this journal, pp. 21-28. Sorption kinetics of chlorinated benzenes from a natural lake sediment have been investigated in gas-purge desorption experiments. Biphasic desorption curves, with an initial "fast" part and a subsequent "slow" part, were found for all tested chlorobenzenes. From these results first-order sorption uptake and desorption rate constants were calculated with a two-sediment compartment model, which is presented in the first paper.In three sets of experiments the sorption uptake period and sediment/water ratio were varied. Rate constants are not influenced by these experimental conditions, which supports the partitioning concept for the sorption of hydrophobic organic chemicals in sediments.

Bioavailability of organic chemicals in the aquatic environment.

1. Bioavailability in the aquatic environment can be defined as the external availability of a chemical to an organism. The availability of sediment-sorbed chemicals to organisms is a particularly important aspect of this phenomena. 2. Various experiments described in the literature, such as toxicity and accumulation experiments, have investigated the influence of suspended sediment in the aqueous phase on bioavailability. 3. The bioavailability of a chemical appears to be influenced by the chemical, the sediment, and the organism being examined. Thus, describing "the bioavailability" of a chemical in the aquatic environment is not a simple process.