S.J.H. Crum

Effects of chronic low concentrations of the pesticides chlorpyrifos and atrazine in indoor freshwater microcosms

Abstract Effects of chronic low concentrations of chlorpyrifos (0.1 μg.L−1) and atrazine (5 μg.L-−1) were studied in indoor freshwater microcosms. Test concentrations were based on a factor of 0.1 multiplied by the lowest available L(E)C50 of standard aquatic test organisms. We tested whether this safety factor was sufficient to protect aquatic communities in the-microcosms in the case of a chronic exposure regime. Effects on plankton, macro-invertebrates and physico-chemical parameters during the seven weeks of treatment are summarized in this paper. Chlorpyrifos treatment resulted in primary effects on the zooplankton taxa Cyclopoida and Daphnia galeata and the macro-invertebrate Gammarus pulex, and secondary effects on the rotifer Keratefia quadrata. No effects of chlorpyrifos on phytoplankton or on physico-chemical parameters were found. Atrazine exposure caused a slight shift in the functional parameters: DO, pH, alkalinity and conductivity, indicating a small decrease in photosynthetic activity. No effects of atrazine on the species composition of the ecosystem were found. In case of a chronic exposure to chlorpyrifos, a safety factor of 0.1 appeared to be insufficient to protect the aquatic community.

Fate and effects of the insecticide Dursban® 4E in indoor Elodea-dominated and macrophyte-free freshwater model ecosystems: I. Fate and primary effects of the active ingredient chlorpyrifos

The fate of the insecticide Dursban® 4E (active ingredient chlorpyrifos) and its effect on crustaceans and insects was studied in indoor experimental freshwater ecosystems that intended to mimick drainage ditches. A single dose (simulating aerial drift) was applied to achieve nominal chlorpyrifos concentrations of 5 or 35 μg/L. Two experiments were performed, one in which all model ecosystems were dominated by the macrophyte Elodea nuttallii, and one using systems devoid of macrophytes.In macrophyte-dominated systems, Elodea vegetation adsorbed a large proportion of the dose applied and hampered the mixing of the insecticide in the water (at least up till day 8). Only a small proportion became incorporated in the sediment. In open water systems the insecticide was rapidly mixed in the water, and the sediment played a very significant role as sink for chlorpyrifos. In both Elodea-dominated and open water systems 50% of the dose applied had disappeared on day 8 post-treatment. The rate of disappearance of chlorpyrifos was relatively rapid in water and macrophytes, and relatively slow in the sediment.Of the arthropods in the zooplankton Cladocera were more susceptible than Copepoda. Significant effects (p⩽0.05) on Cladocera occurred relatively late in Elodea-dominated systems (in week 4 post-application) in contrast to open water systems (week 1), which is in accordance with the observed differences in the fate of chlorpyrifos. Daphnia pulex, D. longispina and Simocephalus vetulus recovered in the model ecosystems when chlorpyrifos concentrations were lower than 0.1–0.2 μg/L, which is in agreement with results of laboratory protocol tests performed with these cladocerans.Among the macroscopic Arthropoda the apparent order of susceptibility was amphipods > insects > isopods. The isopod Asellus aquaticus was more sensitive to the application of the insecticide than the closely related species Proasellus coxalis. In treated open water systems the latter even increased significantly in numbers. Cage experiments in the model ecosystems performed with several species of Arthropoda indicate that laboratory protocol tests may give a reasonable prediction of short-term direct effects of chlorpyrifos for the same species inhabiting more complex aquatic systems.

Accelerated transformation of aldicarb, oxamyl and ethoprophos after repeated soil treatments

Abstract Distribution and transformation of the nematicides aldicarb, oxamyl and ethoprophos was measured on annually treated plots and plots not previously treated on two potato fields. This trial plan was chosen because the effect of the nematicides decreased in the annually treated plots on these fields. In the field, the contents of the nematicides decreased more rapidly in soil of the annually treated plots than in the untreated ones. This rapid disappearance of the active compounds was found to be the cause of the decreased nematode control on the annually treated plots. The considerably more rapid transformation of the nematicides in treated soils than in untreated ones was also measured in incubation tests at 15°C. Sterilization of the treated soils drastically reduced the rates of disappearance. The repeated applications of the nematicides must have induced microbial adaptation, which resulted in accelerated transformation. The carbamoyloximes aldicarb and oxamyl were transformed at about the same rates in previously untreated soils and in soils from plots previously treated with ethoprophos. However, oxamyl was transformed very rapidly in soil previously treated with aldicarb and also aldicarb in soil previously treated with oxamyl: this indicates that cross-adaptation occurred for the two carbamoyloximes.

Effects of a herbicide-insecticide mixture in freshwater microcosms: risk assessment and ecological effect chain.

Effects of chronic application of a mixture of the herbicide atrazine and the insecticide lindane were studied in indoor freshwater plankton-dominated microcosms. The macroinvertebrate community was seriously affected at all but the lowest treatment levels, the zooplankton community at the three highest treatment levels, with crustaceans, caddisflies and dipterans being the most sensitive groups. Increased abundance of the phytoplankton taxa Cyclotella sp. was found at the highest treatment level. Threshold levels for lindane, both at population and community level, corresponded well with those reported in the literature. Atrazine produced fewer effects than expected, probably due to decreased grazer stress on the algae as a result of the lindane application. The safety factors set by the Uniform Principles for individual compounds were also found to ensure protection against chronic exposure to a mixture of a herbicide and insecticide at community level, though not always at the population level.

Aquatic risk assessment of a realistic exposure to pesticides used in bulb crops: a microcosm study.

The fungicide fluazinam, the insecticide lambda-cyhalothrin, and the herbicides asulam and metamitron were applied to indoor freshwater microcosms (water volume approximately 0.6 m3). The treatment regime was based on a realistic application scenario in tulip cultivation. Concentrations of each pesticide were equal to 0%, 0.2%, 0.5%, 2%, and 5% spray drift emission of label-recommended rates. Contribution of compounds to the toxicity of the pesticide package was established by expressing their concentrations as fractions of toxic units. The fate of the compounds in the water, and responses of phytoplankton, zooplankton, periphyton, macroinvertebrates, macrophytes, decomposition, and water quality were followed for 13 weeks. The half-lives of lambda-cyhalothrin, metamitron, and fluazinam were 1 to 2 d; that of asulam was >30 d. No consistent effects could be demonstrated for the 0.2% treatment regime that was therefore considered the no-observed-effect concentration community (NOEC). The macroinvertebrate populations of Gammarus pulex, Asellus aquaticus, and Proasellus meridianus were the most sensitive end points, followed by species of copepods and cladocerans. Responses mainly were due to lambda-cyhalothrin. The 0.5% treatment regime resulted in short-term effects. Pronounced effects were observed at the 2% and 5% treatment levels. At the end of the experiment, the macrophyte biomass that consisted of Elodea nuttallii, showed a decline at the two highest treatment levels, asulam being the causal factor (NOEC: 0.5% treatment level). Primary production was reduced at the 5% treatment level only. In our experiment, the first-tier risk assessment procedure for individual compounds was adequate for protecting sensitive populations exposed to realistic combinations of pesticides. Spray drift reduction measures seem to be efficient in protecting aquatic ecosystems in agricultural areas.

Toxicity of Derosal (active ingredient carbendazim) to aquatic invertebrates

Short- and long-term laboratory single species toxicity tests were performed with eleven invertebrate species and the fungicide Derosal(R) (a.i. carbendazim). Toxicity values differed widely between the tested invertebrates. The most sensitive species we found was the flatworm Dugesia lugubris (96hr-EC50: 25 g/L, 21d-NOEC(reproduction): 11 g/L). Besides within flatworms, other sensitive taxa were representatives of oligochaetes, amphipods and cladocerans. On the longer-term, offspring production of some gastropod species was found to be a relatively sensitive life history characteristic for this latter group.

Effects of a Mixture of Two Insecticides in Freshwater Microcosms: I. Fate of Chlorpyrifos and Lindane and Responses of Macroinvertebrates

Effects of chronic application of a mixture of the insecticides chlorpyrifos and lindane were studied in indoor freshwater microcosms. The exposure concentrations (based on 0, 0.005, 0.01, 0.05, 0.1 and 0.5 times the LC50 of the most sensitive standard test organism for each compound) were kept at a constant level for four weeks. The calculated mean concentrations for chlorpyrifos were found to be almost at their corresponding nominal level during the treatment period. The mean calculated lindane concentrations, however, were found to be 15–40% higher than intended. In the post treatment period both insecticides dissipated fast (t1/2: chlorpyrifos 9 days, lindane 22 days) from the water phase. The concentrations of the mixture at the highest treatment level corresponded to 0.53 toxic units (TU) for Daphnia magna and 0.61 TU for the most sensitive fish. The decomposition of Populus leaves in litter bags was significantly lower at the three highest insecticide concentrations. The macroinvertebrate community was seriously affected at the three highest treatment levels, with Crustacea and the Chironomidae Corynoneura proving to be the most sensitive groups. Gastropoda and Oligochaeta were relatively insensitive and some taxa (e.g. Valvata piscinalis, juvenile Physa fontinalis, Nemertea and Stylaria lacustris) increased in numbers. The observed effects could be explained from the individual toxicity of the insecticides to the invertebrates, and did not indicate synergistic effects. A second paper (Van den Brink et al., 2002) addresses the effects on other endpoints, as well as the overall risk assessment of the insecticide mixture.

Fate and effects of the insecticide chlorpyrifos in outdoor plankton-dominated microcosms in Thailand.

The fate and effects of the insecticide chlorpyrifos were studied in plankton-dominated, freshwater microcosms in Thailand. Disappearance rates of chlorpyrifos from the water column in the present study were similar to those in temperate regions. Insecticide accumulation in the sediment was relatively small, with the major part in the top layer (depth, 1.5 cm). Application of chlorpyrifos led to significant changes in freshwater biological communities. Clam shrimps (Conchostraca) and the cladoceran Moina micrura were the most susceptible species (no-observed-effect concentration [NOEC], 0.1 microg/L) and macroinvertebrates the most sensitive community (NOEC, 0.1 microg/L). These results are in agreement with those from semifield experiments with chlorpyrifos in temperate regions. The results of an in situ bioassay were used to calculate a NOEC of 0.1 microg/L and a 48-h median lethal concentration of 0.6 microg/L for M. micrura, which are similar to toxicity values reported for Daphnia magna in studies in temperate regions. Overall, these findings support the use of toxicity data from temperate regions for the risk assessment of low-persistent insecticides like chlorpyrifos for aquatic communities in tropical regions.

Responses of zooplankton in lufenuron‐stressed experimental ditches in the presence or absence of uncontaminated refuges

Outdoor experimental ditches were used to evaluate the influence of untreated refuges on the recovery of zooplankton communities following treatment with the fast-dissipating insecticide lufenuron. Each experimental ditch was divided into three sections of the same surface area. The treatments differed in the proportion of ditch (0, 33, 67, and 100% of the surface area) to which the insecticide was applied at the same nominal treatment (3 mug/L). During the first week postapplication, a barrier was placed between treated and untreated ditch sections. The untreated sections were included to provide a source of organisms for recovery of affected zooplankton populations in the treated sections of the ditch after the removal of the barrier. Cyclopoida were the most affected by lufenuron treatment, followed by Daphnia gr. galeata. These and other direct effects of treatment on larvae of the phantom midge Chaoborus spp. resulted in clear indirect effects on populations of Calanoida, Ceriodaphnia, and Rotifera. Overall, faster recovery of the zooplankton community was observed in the treated sections of ditches that were sprayed for a smaller proportion of their surface area. Nevertheless, individual zooplankton populations showed considerable differences in rate of recovery. Cyclopoida showed a relatively slow rate of recovery even in the partially treated ditches. Daphnia gr. galeata recovered more rapidly in treated ditch sections in the presence of unsprayed ditch sections, illustrating the potential influence of unexposed refuges. Furthermore, the presence of refuges most likely dampened the magnitude and duration of indirect effects in the ditches treated with lufenuron.

Estimating degradation rates in outdoor stagnant water by inverse modelling with TOXSWA: a case study with prosulfocarb

BACKGROUND The regulatory risk assessment of pesticides requires the assessment of exposure of aquatic ecosystems in small surface waters adjacent to agricultural fields. This exposure is predicted using simulation models, for which an important input parameter is the degradation rate in water. In regulatory dossiers, the decline rate in water from outdoor mesocosms is often available, but this rate encompasses more processes than degradation. Therefore, a procedure was designed for estimating the degradation rate in water that was suitable for mesocosm studies with limited datasets, e.g. datasets lacking site-specific sorption coefficients and relevant sediment properties. The procedure, based upon inverse modelling with TOXSWA, has been tested on a dataset for prosulfocarb in stagnant ditches. RESULTS A degradation half-life in the ditch water of 2.9 days (20 °C) was found. This short half-life was to a significant extent accounted for by biodegradation rather than hydrolysis or photolysis. This half-life was considerably shorter than the half-life in the water layer of two laboratory water-sediment system experiments. CONCLUSION The estimation procedure resulted in a unique half-life for the degradation rate in water. Such outdoor mesocosm studies seem to be better suited to assessing the degradation rate in water in ditches than the conventional water-sediment studies.