Michiel A. Daam

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.

Ecological effects of the herbicide linuron in tropical freshwater microcosms.

Effects of a single application of the photosynthesis-inhibiting herbicide linuron (0, 15, 50, 150, and 500 microg/L) on the ecology of outdoor plankton-dominated microcosms were studied in Thailand. As a result of the decreased photosynthesis, DO and pH decreased while EC, alkalinity and nutrient concentrations increased. Chlorophytes belonging to the genera Scenedesmus, Coelastrum and Pediastrum were the most sensitive taxa, whereas several other chlorophytes, diatoms, and cryptophytes increased in abundance. Tolerant taxa appeared to be less digestable for several zooplankton taxa, which subsequently decreased in abundances. Chamaesiphon sp. (Cyanobacteria) was the most susceptible periphyton species. As a consequence of functional redundancy, effects of the herbicide on the chlorophyll-a content of periphyton and especially phytoplankton did not always reflect the effects noted on community level.

Sensitivity of macroinvertebrates to carbendazim under semi-field conditions in Thailand: Implications for the use of temperate toxicity data in a tropical risk assessment of fungicides

The present paper discusses the fate of the fungicide carbendazim (nominal concentrations: 0, 3.3, 33, 100 and 1000 microg L(-1)) and its effects on the macroinvertebrate community in outdoor microcosms set up in Thailand. Fate and threshold values were subsequently compared with those noted in temperate model ecosystem studies in order to evaluate to which extent toxicity data generated in temperate regions for compounds like carbendazim may be extrapolated to tropical areas. Carbendazim disappeared faster from the water column than reported in temperate model ecosystem studies, which is explained by a possibly greater microbial breakdown of the fungicide under the tropical conditions tested. The No Observed Effect Concentration (NOEC) calculated in the present study for the macroinvertebrate community was the same as recorded in a study carried out in The Netherlands (3.3 microg L(-1)). However, most sensitive representatives in the latter study were worm-like taxa, whereas water boatmen (Corixidae) were the most sensitive macroinvertebrates in the present study. The ecological realism of a tropical risk assessment based on temperate organisms that are less sensitive than local macroinvertebrates may be questionable. Recommendations for future research include testing the possibility to rear sensitive representatives of indigenous Thai Corixidae in the laboratory and conducting model ecosystem studies evaluating a wider range of pesticides on a larger tropical geographical scale.

Comparison of fate and ecological effects of the herbicide linuron in freshwater model ecosystems between tropical and temperate regions.

This paper compares the fate and effects of linuron in an outdoor plankton-dominated microcosm study carried out in Thailand with those reported in temperate model ecosystem studies evaluating linuron and other photosynthesis-inhibiting herbicides. Lower linuron concentrations disappeared slightly faster from the water compartment compared to temperate conditions, which appears to be related with the experimental design rather than differences in climatic conditions. Sensitivity of primary producers and zooplankton were similar for the climatic regions, whereas effects on ecosystem functioning were less pronounced in tropical microcosms. Recovery potential of affected endpoints appears higher for tropical ecosystems compared to their temperate counterparts. These findings support the use of toxicity data generated in temperate countries in the tropics. Recommendations for the methodology of tropical model ecosystem experiments are discussed.

Direct and Indirect Effects of the Fungicide Carbendazim in Tropical Freshwater Microcosms

Direct and indirect effects of the fungicide carbendazim on ecosystem structure and functioning were studied ≤8xa0weeks after application (nominal concentrations: 0, 3.3, 33, 100, and 1000xa0μg/L) to outdoor microcosms in Thailand. Direct effects on macroinvertebrates are discussed in detail in a separate article. The present article presents the effects on other end points and discusses the hypothesized ecologic effect chain. Negative treatment effects on the zooplankton community were only recorded for the highest carbendazim treatment (NOECcommunityxa0=xa0100xa0μg/L). The rotifer Keratella tropica, cladocerans (Moina micrura, Ceriodaphnia cornuta, and Diaphanosoma sp.), and cyclopoid copepods were decreased or even eliminated at this treatment level. The decrease in zooplankton and macroinvertebrate abundances was accompanied by an increase in numbers of several tolerant invertebrates, presumably caused by a release from competition and predation. The death of sensitive invertebrates probably also led to an overall decreased grazing pressure because increased levels of chlorophyll-a and bloom of the floating macrophyte Wolffia sp. were noted. The increase in primary producers is discussed to be the probable cause of changes in physicochemical water conditions, eventually resulting in an anoxic water layer during the last 3xa0weeks of the experiment. This is likely to have resulted in decreased invertebrate abundances noted in that period. Furthermore, the decreased decomposition of Musa (banana) leaves observed 8xa0weeks after application is considered to be the indirect effect of a decreased microbial activity resulting from these anoxic water conditions, rather than a direct toxic effect of carbendazim.

Impact of single and repeated applications of the insecticide chlorpyrifos on tropical freshwater plankton communities

This paper describes the effects of a single and a repeated application of the organophosphorus insecticide chlorpyrifos on zooplankton and phytoplankton communities in outdoor microcosms in Thailand. Treatment levels of 1xa0μgxa0L−1 were applied once or twice with a 2-week interval. Both treatments led to a significant decrease in cladocerans followed by an increase in rotifers, although the extent by which species were affected was different. Ceriodaphnia cornuta was the most responding cladoceran after the first treatment, while Moina micrura responded most to the second. This is explained by differences in the growth phase of M.xa0micrura at the time of application and an increase in Microcystis abundance over the course of the experiment. Several phytoplankton taxa either increased or decreased as a result of the chlorpyrifos-induced changes in zooplankton communities. Even though chlorpyrifos disappeared fast from the water column, effects on plankton communities persisted till the end of the experiment (42xa0days) when the insecticide concentrations had dropped below the detection limit. This was presumably due to the increasing population trend of Microcystis, favouring rotifers over cladocerans.

Acute toxicity of zinc and arsenic to the warmwater aquatic oligochaete Branchiura sowerbyi as compared to its coldwater counterpart Tubifex tubifex (Annelida, Clitellata)

PurposeThis study aimed at evaluating the acute effects of arsenic and zinc to the warmwater aquatic oligochaete Branchiura sowerbyi. Relative sensitivity with the coldwater species Tubifex tubifex was compared. Implications for the use of B. sowerbyi in the risk assessment of sediments in the tropics are discussed.Materials and methodsWater-only (96xa0h) and sediment (14xa0days) toxicity tests were conducted with both species evaluating a concentration series of arsenic and zinc. The tests were conducted considering the environmental conditions in the natural habitat of T. tubifex (predominantly temperate) and B. sowerbyi (predominantly tropical). Both lethal and sublethal endpoints (autotomy of the posterior body parts, abnormal behavior and appearance) were determined in the tests. The lethal (LC10 and LC50) and effect (EC10 and EC50) concentrations were also determined to assess metal sensitivity for both species.Results and discussionBoth test species were more sensitive to Zn than As in water-only tests, which is in agreement with previous studies evaluating the toxicity of these metals to aquatic oligochaetes. Sublethal effects were generally noted at concentrations lower than those leading to mortality. The warmwater oligochaete B. sowerbyi was more sensitive to both metals tested than the coldwater species T. tubifex.ConclusionsStudy findings support the need for using indigenous tropical species in risk assessments in the tropics. In addition, sublethal effect parameters should be included in toxicity testing with aquatic oligochaetes.

The use of gene expression to unravel the single and mixture toxicity of abamectin and difenoconazole on survival and reproduction of the springtail Folsomia candida

Pesticides risk assessments have traditionally focused on the effects on standard parameters, such as mortality, reproduction and development. However, one of the first signs of adverse effects that occur in organisms exposed to stress conditions is an alteration in their genomic expression, which is specific to the type of stress, sensitive to very low contaminant concentrations and responsive in a few hours. The aim of the present study was to evaluate the single and binary mixture toxicity of commercial products of abamectin (Kraft® 36u202fEC) and difenoconazole (Score® 250u202fEC) to Folsomia candida. Laboratory toxicity tests were conducted to access the effects of these pesticides on springtail survival, reproduction and gene expression. The reproduction assays gave EC50 and EC10 values, respectively, of 6.3 and 1.4u202fmg a.s./kg dry soil for abamectin; 1.0 and 0.12u202fmg a.s./kg dry soil for Kraft® 36u202fEC; and 54 and 23u202fmg a.s./kg dry soil for Score® 250u202fEC. Technical difenoconazole did not have any effect at the concentrations tested. No significant differences in gene expression were found between the abamectin concentrations tested (EC10 and EC50) and the solvent control. Exposure to Kraft® 36u202fEC, however, significantly induced Cyp6 expression at the EC50 level, while VgR was significantly downregulated at both the EC10 and EC50. Exposure to the simple pesticide mixture of Kraft® 36xa0ECxa0+xa0Score® 250u202fEC caused significant up regulation of ABC transporter, and significant down regulation of VgR relative to the controls. GABA receptor also showed significant down-regulation between the EC10 and EC50 mixture treatments. Results of the present study demonstrate that pesticide-induced gene expression effects precede and occur at lower concentrations than organism-level responses. Integrating omic endpoints in traditional bioassays may thus be a promising way forward in pesticide toxicity evaluations.

Chironomus sancticaroli (Diptera, Chironomidae) as a Sensitive Tropical Test Species in Laboratory Bioassays Evaluating Metals (Copper and Cadmium) and Field Testing

Despite that chironomids are the most widely used benthic insect test species worldwide, little research has been conducted so far with tropical chironomid representatives. This study was designed to evaluate the indigenous midge Chironomus sancticaroli as a candidate test species for use in tropical toxicity assessments. To this end, laboratory water-only toxicity tests were conducted evaluating copper and cadmium. Obtained lethal concentration values were overall comparable or lower than those reported for other chironomids, including those most commonly used in temperate regions (C. riparius and C. dilutus). In addition, C. sancticaroli was deployed in situ in the Monjolinho River (São Paulo State, Brazil), and toxicity of sediment from this river was evaluated in the laboratory. Several field water and sediment quality parameters also were measured to enable correlating these with the effects observed in these toxicity tests. Field sediment toxicity to C. sancticaroli appeared to be related with sediment endosulfan concentrations, whereas effects noted in the in situ test were likely due to low pH values measured in river water. Chironomus sancticaroli appears to be a suitable candidate for inclusion as a test species in tropical toxicity evaluations in both the laboratory and the field.