Francisco Sánchez-Bayo

Detection and analysis of neonicotinoids in river waters--development of a passive sampler for three commonly used insecticides.

Increasing and widespread use of neonicotinoid insecticides all over the world, together with their environmental persistence mean that surface and ground waters need to be monitored regularly for their residues. However, current multi-residue analytical methods for waters are inadequate for trace residue analysis of these compounds, while passive sampling devices are unavailable. A new method using UltraPerformance Liquid Chromatography provided good separation of the five most common neonicotinoid compounds, with limits of quantitation in the range 0.6-1.0ng. The method was tested in a survey of rivers around Sydney (Australia), where 93% of samples contained two or more neonicotinoids in the range 0.06-4.5μgL(-1). Styrenedivinylbenzene-reverse phase sulfonated Empore™ disks were selected as the best matrix for use in passive samplers. Uptake of clothianidin, imidacloprid and thiacloprid in a flow-through laboratory system for 3weeks was linear and proportional to their water concentrations over the range 1-10μgL(-1). Sampling rates of 8-15mLd(-1) were correlated to the hydrophobicity of the individual compounds. The passive samplers and analytical methods presented here can detect trace concentrations of neonicotinoids in water.

Cumulative ecological impacts of two successive annual treatments of imidacloprid and fipronil on aquatic communities of paddy mesocosms.

Agricultural landscapes, including paddies, play an important role in maintaining biodiversity, but this biodiversity has been under the threat of toxic agro-chemicals. Our knowledge about how aquatic communities react to, and recover from, pesticides, particularly in relation to their residues, is deficient, despite the importance of such information for realistic environmental impact assessment of pesticides. The cumulative ecological impacts on aquatic paddy communities and their recovery processes after two successive annual applications of two systemic insecticides, imidacloprid and fipronil, were monitored between mid-May and mid-September each year. The abundance of benthic organisms during both years was significantly lower in both insecticide-treated fields than in the controls. Large-impacts of fipronil on aquatic arthropods were found after the two years. Growth of medaka fish, both adults and their juveniles, was affected by the application of the two insecticides. A Principal Response Curve analysis (PRC) showed the escalation and prolongation of changes in aquatic community composition by the successive annual treatments of each insecticide over two years. Residues of fipronil in soil, which are more persistent than those of imidacloprid, had a high level of impact on aquatic communities over time. For some taxonomic groups, particularly for water surface-dwelling and water-borne arthropods, the second annual treatment had far greater impacts than the initial treatment, indicating that impacts of these insecticides under normal use patterns cannot be accurately assessed during short-term monitoring studies, i.e., lasting less than one year. It is concluded that realistic prediction and assessment of pesticide effects at the community level should also include the long-term ecological risks of their residues whenever these persist in paddies over a year.

The molecular basis of simple relationships between exposure concentration and toxic effects with time

Understanding the toxicity of chemicals to organisms requires considering the molecular mechanisms involved as well as the relationships between exposure concentration and toxic effects with time. Our current knowledge about such relationships is mainly explained from a toxicodynamic and toxicokinetic perspective. This paper re-introduces an old approach that takes into account the biochemical mode of action and their resulting biological effects over time of exposure. Empirical evidence demonstrates that the Druckrey-Küpfmüller toxicity model, which was validated for chemical carcinogens in the early 1960s, is also applicable to a wide range of toxic compounds in ecotoxicology. According to this model, the character of a poison is primarily determined by the reversibility of critical receptor binding. Chemicals showing irreversible or slowly reversible binding to specific receptors will produce cumulative effects with time of exposure, and whenever the effects are also irreversible (e.g. death) they are reinforced over time; these chemicals have time-cumulative toxicity. Compounds having non-specific receptor binding, or involving slowly reversible binding to some receptors that do not contribute to toxicity, may also be time-dependent; however, their effects depend primarily on the exposure concentration, with time playing a minor role. Consequently, the mechanism of toxic action has important implications for risk assessment. Traditional risk approaches cannot predict the impacts of toxicants with time-cumulative toxicity in the environment. New assessment procedures are needed to evaluate the risk that the latter chemicals pose on humans and the environment. An example is shown to explain how the risk of time-dependent toxicants is underestimated when using current risk assessment protocols.

Differences in ecological impacts of systemic insecticides with different physicochemical properties on biocenosis of experimental paddy fields

The environmental risks of pesticides are typically determined by laboratory single-species tests based on OECD test guidelines, even if biodiversity should also be taken into consideration. To evaluate how realistic these assessments are, ecological changes caused by the systemic insecticides imidacloprid and fipronil, which have different physicochemical properties, when applied at recommended commercial rates on rice fields were monitored using experimental paddy mesocosms. A total of 178 species were observed. There were no significant differences in abundance of crop arthropods among the experimental paddies. However, zooplankton, benthic and neuston communities in imidacloprid-treated field had significantly less abundance of species than control and fipronil fields. Significant differences in abundance of nekton community were also found between both insecticide-treated paddies and control. Influences on the growth of medaka fish were also found in both adults and their fries. Both Principal Response Curve analysis (PRC) and Detrended Correspondence Analysis (DCA) showed the time series variations in community structure among treatments, in particular for imidacloprid during the middle stage of the experimental period. These results show the ecological effect-concentrations (LOECxa0~xa01xa0μg/l) of these insecticides in mesocosms, especially imidacloprid, are clearly different from their laboratory tests. We suggest that differences in the duration of the recovery process among groups of species are due to different physicochemical properties of the insecticides. Therefore, realistic prediction and assessment of pesticide effects at the community level should consider not only the sensitivity traits and interaction among species but also the differences in physicochemical characteristics of each pesticide.

From simple toxicological models to prediction of toxic effects in time

The ability to predict the effects of toxicants in organisms with reasonable accuracy depends to a great extent on the toxico-kinetic models used to describe such effects. Toxic effects of organic chemicals and heavy metals have been described adequately using a hyperbolic model that considers the concentration of the toxicant and the time of exposure only. Such a model relies on the median time to effect (ET50) of a chemical to estimate effects at any exposure time, but cannot make predictions for concentrations other than those tested experimentally. A complementary log-to-log model can calculate all ET50 values for a toxicant, thus enabling the hyperbolic model to predict any level of effect for any combination of concentrations and times of exposure. The parameter values used in both models are obtained from experimental bioassays where the time-to-effect of a toxicant is recorded regularly in addition to standard acute or chronic toxicity data. These models will facilitate the risk assessment of chemicals by (1) predicting effects under any combination of time and concentrations, and (2) reducing to a minimum the experimental efforts required to obtain comprehensive ecotoxicity data.

Differences in susceptibility of five cladoceran species to two systemic insecticides, imidacloprid and fipronil

Differences in susceptibility of five cladocerans to the neonicotinoid imidacloprid and the phenyl-pyrazole fipronil, which have been dominantly used in rice fields of Japan in recent years, were examined based on short-term (48-h), semi-static acute immobilization exposure tests. Additionally, we compared the species sensitivity distribution (SSD) patterns of both insecticides between two sets of species: the five tested cladocerans and all other aquatic organisms tested so far, using data from the ECOTOX database of U.S. Environmental Protection Agency (USEPA). The sensitivity of the test species to either imidacloprid or fipronil was consistent, spanning similar orders of magnitude (100 times). At the genus level, sensitivities to both insecticides were in the following descending order: Ceriodaphniaxa0>xa0Moinaxa0>xa0Daphnia. A positive relationship was found between body lengths of each species and the acute toxicity (EC50) of the insecticides, in particular fipronil. Differences in SSD patterns of imidacloprid were found between the species groups compared, indicating that test cladocerans are much less susceptible than other aquatic species including amphibians, crustaceans, fish, insects, mollusks and worms. However, the SSD patterns for fipronil indicate no difference in sensitivity between cladocerans tested and other aquatic organisms despite the greater exposure, which overestimates the results, of our semi-static tests. From these results, Ceriodaphnia sp. should be considered as more sensitive bioindicators (instead of the standard Daphnia magna) for ecotoxicological assessments of aquatic ecosystems. In addition, we propose that ecotoxicity data associated with differences in susceptibility among species should be investigated whenever pesticides have different physicochemical properties and mode of action.

Comparison of environmental risks of pesticides between tropical and nontropical regions

A comparison of environmental risks of pesticides between tropical and nontropical regions has been performed, using data from the literature and modeling outputs based on the physicochemical properties of the compounds. With a few exceptions, the level of risk of exposure for most pesticides in tropical agriculture is similar to that in other climatic regions of the world. Generally, dissipation of pesticides increases under the warm and wet conditions of the tropics, with most of the dissipation occurring through hydrolysis in water and biological degradation in water and soil. High temperatures in the tropics also foster volatilization rates, whereas high precipitation and poor soils tend to increase losses into runoff and, for certain chemicals, affects their leaching behavior. The environmental risk is determined by a balance of soil types, soil organic carbon, pH, and the rates of degradation in the various environmental compartments.

An amperometric method for the detection of amitrole, glyphosate and its aminomethyl-phosphonic acid metabolite in environmental waters using passive samplers.

The herbicides amitrole and glyphosate, and its metabolite aminomethyl-phosphonic acid (AMPA), in water samples have been directly analysed by high-performance liquid chromatography using an electrochemical (EC) detector. Limits of detection of 0.3 microg mL(-1) for glyphosate, 0.05 microg mL(-1) for AMPA and 0.03 microg mL(-1) for amitrole were comparable to those obtained by other authors using EC and also by liquid chromatography coupled to mass spectrometry, but the latter method requires derivatisation and pre-concentration of the sample whereas EC methods show similar sensitivity without the need of any derivatisation. The method was specifically designed to analyse extracts from passive samplers used for monitoring of polar herbicide residues in waters. To this purpose, three types of Empore disks were tested for their ability to adsorb and desorb these ionic, polar analytes. A procedure for their extraction from the membranes and reducing the interferences from other substances present in natural waters (i.e. humic acids) is described. The method is simple, does not require sophisticated equipment and is valid for the analysis and monitoring of herbicides residues using passive samplers.

Impact of Systemic Insecticides on Organisms and Ecosystems

Systemic insecticides were first developed in the 1950s, with the introduction of soluble or‐ ganophosphorus (OP) compounds such as dimethoate, demeton-S-methyl, mevinphos and phorate. They were valuable in controlling sucking pests and burrowing larvae in many crops, their main advantage being their translocation to all tissues of the treated plant. Sys‐ temic carbamates followed in the 1960s with aldicarb and carbofuran. Since then, both insec‐ ticidal classes comprise a large number of broad-spectrum insecticides used in agriculture all over the world. Nowadays, OPs are the most common pesticides used in tropical, devel‐ oping countries such as the Philippines and Vietnam, where 22 and 17% of the respective agrochemicals are ‘extremely hazardous’ [126], i.e. classified as WHO class I. Systemic insect growth regulators were developed during the 1980-90s, and comprise only a handful of compounds, which are more selective than their predecessors. Since 1990 onwards, cartap, fipronil and neonicotinoids are replacing the old hazardous chemicals in most developed and developing countries alike [137].

FATTY ACID COMPOSITION OF THE ESTUARINE AMPHIPOD, MELITA PLUMULOSA (ZEIDLER): LINK BETWEEN DIET AND FECUNDITY

The influence of various diets on the survival, fecundity, and the polyunsaturated fatty acid (PUFA) composition of the benthic estuarine amphipod Melita plumulosa (Zeidler) in laboratory cultures were determined. Apart from a natural silty sediment, six commercial food supplements were examined: an omega-6 PUFA enriched Spirulina-based dry powder, Sera micron; a shrimp-based pellet food; an omega-3 PUFA enriched algal paste, Rotiselco-ALG; an omega-6 PUFA enriched algal dry powder, AlgaMac-ARA (arachidonic acid); flaxseed meal; and an omega-3 PUFA enriched dry powder, Frippak. We have previously established that M. plumulosa cultures perform poorly and eventually decline if provided with silty sediment alone, but will thrive if supplemented with Sera micron. Conversely, if the amphipods are cultured on a nutrient-depleted sand substrate, Sera micron alone does not constitute an adequate feed. The major difference in the fatty acid composition of M. plumulosa cultured on silty sediment compared to amphipods cultured on a sand substrate and both fed Sera micron was an increase in the ratio of omega-3 to omega-6 PUFAs, indicating that the silty sediment provides additional food sources rich in omega-3 PUFAs. Furthermore, amphipods cultured in sand and fed any of the three algal-based foods or the Frippak powder as the sole food source had poor survival rates, although Sera micron maintained the best survival-this was attributed to it containing high amounts of beta-carotene and terpenoids. Melita plumulosa fed a mixture of Sera micron in conjunction with the omega-3 PUFA enriched Rotiselco-ALG and cultured on a silty substrate were found to have good fecundity with low variability.