Impact of a pulse application of permethrin on the macroinvertebrate community of a headwater stream

Active and passive spatial avoidance by aquatic organisms from environmental stressors: A complementary perspective and a critical review

Spatial avoidance is a mechanism by which many organisms prevent their exposure to environmental stressors, namely chemical contaminants. Numerous studies on active avoidance and drift by aquatic organisms, as well as the main approaches used to measure both responses, were reviewed. We put forward a particular recommendation regarding methodological approaches: active avoidance should preferably be evaluated under a dilution gradient in a multi-compartmented system instead of in a bi-compartmented system. Available data on spatial avoidance from contamination indicate that emigration can occur at even lower contaminant concentrations than sub-individual noxious effects (assessed with the traditional forced-exposure assays), challenging the widely accepted paradigm in ecotoxicology that contaminant-driven adverse consequences at the population level result from a time delayed cascade of sequentially linked biochemical, cellular, physiological, and finally whole organism deleterious effects. Therefore, contaminants should not be viewed solely as potential toxicants at the individual level, but also as potential disturbers of habitats, by making the latter, at least partially, unsuited to accommodate life. Also, exposure to contamination is needed to trigger avoidance, but uptake is not mandatory, which demands the concept of exposure to be expanded, to include also the mere perception of the stressor. Since emigration eventually leads to local population extinction, and thus to severe implications for ecosystem structure and functioning, we then recommend that avoidance data be incorporated in environmental risk assessment schemes.

Contaminants as habitat disturbers: PAH-driven drift by Andean paramo stream insects

Contaminants can behave as toxicants, when toxic effects are observed in organisms, as well as habitat disturbers and fragmentors, by triggering avoidance responses and generating less- or uninhabited zones. Drift by stream insects has long been considered a mechanism to avoid contamination by moving to most favorable habitats. Given that exploration and transportation of crude oil represent a threat for surrounding ecosystems, the key goal of the present study was to assess the ability of autochthonous groups of aquatic insects from the Ecuadorian paramo streams to avoid by drift different concentrations of polycyclic aromatic hydrocarbons (PAH) contained in the soluble fraction of locally transported crude oil. In the laboratory, different groups of insects were exposed to PAH for 12h. Three different assays, which varied in taxa and origin of the organisms, concentrations of PAH (0.6-38.8µgL(-1)), and environment settings (different levels of refuge and flow) were performed. For Anomalocosmoecus palugillensis (Limnephilidae), drift was a major cause of population decline in low concentration treatments but at higher concentrations mortality dominated. PAH was highly lethal, even at lower concentrations, for Chironomidae, Grypopterygidae (Claudioperla sp.) and Hydrobiosidae (Atopsyche sp.), and, therefore, no conclusion about drift can be drawn for these insects. Contamination by PAH showed to be a threat for benthic aquatic insects from Ecuadorian paramo streams as it can cause a population decline due to avoidance by drift and mortality.

Effects of repeated insecticide pulses on macroinvertebrate drift in indoor stream mesocosms

Pesticide contaminations via run-off or spray drift have been reported to result in the mass drift of macroinvertebrates as well as causing structural and functional changes of the corresponding stream sections. However, pesticide pulses in the field are associated with sudden increases in flow velocity, water turbidity, and changes in water temperature, which can also induce drift. Only through replicated community testing under highly controlled conditions can these effects be disentangled. In a stream mesocosm study, 12-h pulses of 12 μg/L imidacloprid were set three times at weekly intervals and are considered a "pulse series". Two pulse series of this neonicotinoid insecticide were run in both spring and summer with 4 treatment and 4 control stream mesocosms used in each pulse series. Prior to the start of the mesocosm experiment, both pulse concentration and duration had been screened for drift responses in larval Baetidae, Chironomidae and adult Gammarus roeseli in laboratory experiments. In the subsequent mesocosm study, each pulse caused a pronounced increase in the drift of insect larvae and gammarids. The drift response was taxon-specific, which was related to preferred habitat and exposure to other stressors like current velocity, in addition to imidacloprid sensitivity. Activity measurements employing a Multispecies Freshwater Biomonitor(®) revealed that in Baetis sp. the diurnal activity pattern became more pronounced even 12h after the pulse though with slightly decreased mean physical activity. Adult G. roeseli showed a drastic pulse by pulse decrease in physical activity which after the 3rd pulse lasted longer than 24h. In conclusion, drift is a sensitive, ecologically relevant endpoint and should be regarded when a specific risk assessment for lotic surface waters is done, e.g. in the context of a spatially explicit risk assessment.

Local physical habitat quality cloud the effect of predicted pesticide runoff from agricultural land in Danish streams

The combination of intensive agricultural activities and the close connectivity between land and stream emphasise the potential risk of pesticide exposure in Danish streams. Benthic macroinvertebrates are applied in the assessment of stream ecological status, and some sensitive species have been shown to respond strongly to brief pulses of pesticide contamination. In this study we investigate the impact of agriculturally derived pesticides on stream macroinvertebrate communities in Denmark. As a measure of toxic pressure we apply the Runoff Potential. We investigated a total of 212 streams. These were grouped into distinct classes according to the magnitude of pesticide contamination in the period from 2003-2006. A total of 24 different macroinvertebrate indices were applied to detect effects of pesticide runoff (e.g. the SPEAR-index and the number of EPT taxa). We found high predicted pesticide runoff in 39% of the streams, but we found no significant effect of predicted pesticide exposure on stream macroinvertebrate indices. We, additionally, examined the influence of a series of environmental parameters ranging from site scale to catchment scale on the macroinvertebrate community. Relative proportions of gravel, sand and silt in bed sediments explained most of the variation in macroinvertebrate indices as well as the upstream riparian habitat quality. We suggest that the Runoff Potential model overestimate pesticide runoff contamination in Danish streams due the presence of buffer strips enforced by Danish legislation. When pesticide runoff contamination is low to moderate, poor physical properties (indirectly related to agricultural activity) are the main impediment for the ecological quality of Danish streams.

Gammarus spp. in aquatic ecotoxicology and water quality assessment: toward integrated multilevel tests

The amphipod genus Gammarus is widespread and is structurally and functionally important in epigean freshwaters of the Northern Hemisphere. Its presence is crucial, because macroinvertebrate feeding is a major rate-limiting step in the processing of stream detrius. In addition, Gammarus interacts with multiple trophic levels bu functioning as prey, predator, herbivore, detritivore, and shredder. Such a broad span of ecosystem participation underlines the importance of Gammarus to pollutants and other disturbances may render it a valuable indicator for ecosystem health. This review summarizes the vast number of studies conducted with Gammarus spp. for evaluating aquatic ecotoxicology endpoints and examines the suitability of this native invertabrate species for the assessment of stream ecosystem health in the Northern Hemisphere. Numerous papers have been published on how pollutants affect gammarind behavior (i.e., mating, predator avoidance), reproduction, development, feeding activity, population structure, as well as the consequences of pollution on host-parasite, predator-prey, or native-invasive species interactions. Some biochemical and molecular biomarkers have already been established, such as the measurement of vitellogenin-like proteins, metallothioneins, alkali-labile phosphates (in proteins), and lipogenic enzyme activities for assessing endocrine distribution and detoxification mechanisms.

Pesticide alters habitat selection and aquatic community composition

Anthropogenic chemical contamination is an important issue for conservation of aquatic ecosystems. While recent research highlights that community context can mediate the consequences of contaminant exposure, little is known about how contaminants themselves might determine this context by altering habitat selection and thus initial community composition. Here we show that the insecticide carbaryl and its commercial counterpart Sevin can affect aquatic community composition by differentially altering oviposition and colonization of experimental pools by amphibians and insects. On average, contaminated pools received 20-fold more adult beetle and heteropteran colonists and 12-fold more Culex mosquito and chironomid midge egg masses. On the other hand, ovipositing Anopheles mosquitoes and cricket frogs showed no preference and we have shown previously that gray treefrogs strongly avoid contaminated pools. Overall, initial richness doubled in contaminated pools compared with controls. By affecting colonizing taxa differently and increasing richness, the contaminant may alter the ecological context under which subsequent effects of exposure will unfold. Given that community context is important for evaluating toxicity effects, understanding the net effects of contaminants in natural systems requires an understanding of their effects on community assembly via shifts in habitat selection.

Spray drift of pesticides and stream macroinvertebrates: experimental evidence of impacts and effectiveness of mitigation measures

Impoverished stream communities in agricultural landscapes have been associated with pesticide contamination, but conclusive evidence of causality is rare. We address this deficiency by adopting an experimental approach to investigate the effects of the insecticides cypermethrin and chlorpyrifos on benthic macroinvertebrates. Three treatments were established and a combination of biomarker, bioassay and biomonitoring approaches was employed to investigate, individual, population and community-level effects. Animals deployed during pesticide application had altered enzyme activity, depressed feeding rate and reduced survival, but these effects were only observed where pesticide was sprayed to the stream edge. There were no clear pesticide-related effects on macroinvertebrate community structure or on the population densities of individual species. Hence, short-term pesticide exposure did cause individual-level effects in stream macroinvertebrates, but these were not translated to effects at the population or community-level and were effectively mitigated by the adoption of a no-spray buffer zone.

Impact of lambda-cyhalothrin on a macroinvertebrate assemblage in outdoor experimental channels: implications for ecosystem functioning

In this study, the impact of a single pulse of the pyrethroid lambda-cyhalothrin was tested on a macroinvertebrate assemblage consisting of Gammarus pulex, Leuctra nigra, Heptagenia sulphurea and Ancylus fluviatilis in outdoor experimental stream channels. Channels (4m long, 0.1m wide) were groundwater fed and had natural substratum. Macroinvertebrates were exposed to 10.65 or 106.5 ng L(-1) lambda cyhalothrin for 90 min in the laboratory and after 24h introduced to the experimental stream channels with four replicates of each treatment and controls. Drift samples were taken with 24-h interval for 10 days and behaviour of drifted macroinvertebrates was assessed. Microalgae biomass was measured on days 1, 5, 8 and 10 along with leaf litter decomposition using leaf packs of beech (Fagus sylvatica). Numbers of drifting G. pulex and L. nigra with reduced mobility increased significantly with concentration of lambda-cyhalothrin. Increase of algal biomass was significantly greater in stream channels with macroinvertebrates exposed to 106.5 ng L(-1) compared to controls and 10.65 ng L(-1) treatments. Accrual of microalgal biomass was significantly higher in the high concentration treatment and decomposition of leaf litter was significantly greater in control channels compared to channels with exposed macroinvertebrates. This study may apply valuable knowledge to the understanding and assessment of how pyrethroids impact ecosystem functioning in streams.

Field and laboratory simulations of storm water pulses: behavioural avoidance by marine epifauna

Epifaunal communities associated with macroalgae were exposed to storm water pulses using a custom made irrigation system. Treatments included Millipore freshwater, freshwater spiked with trace metals and seawater controls to allow for the relative importance of freshwater inundation, trace metals and increased flow to be determined. Experimental pulses created conditions similar to those that occur following real storm water events. Brief storm water pulses reduced the abundance of amphipods and gastropods. Freshwater was the causative agent as there were no additional effects of trace metals on the assemblages. Laboratory assays indicated that neither direct nor latent mortality was likely following experimental pulses and that epifauna readily avoid storm water. Indirect effects upon epifauna through salinity-induced changes to algal habitats were not found in field recolonisation experiments. Results demonstrate the importance of examining the effects of pulsed contaminants under realistic exposure conditions and the need to consider ecologically relevant endpoints.

Scenario-based simulation of runoff-related pesticide entries into small streams on a landscape level

The prediction of runoff-related pesticide entry into surface waters on a landscape level usually requires considerable efforts with regard to input data, time, and personnel. Therefore, the need for an easy to use simulation tool with easily accessible input data, for example from already existing public sources, is obvious. In this paper, we present a simulation tool for the simulation of pesticide entry from arable land into adjacent streams. Our aim was to develop a tool applicable on the landscape level using "real world data" from numerous sites and for the simulation of parameter case studies concerning particular parameters at single sites. We used the ratio of exposure to toxicity (REXTOX) model proposed by the OECD, which had been successfully validated in the study area as part of a previous study and which was extended to calculate pesticide concentrations in adjacent streams. We simulated the pesticide entry on the landscape level at 737 sites in small streams situated in the central lowland of Germany with winter wheat, barley, and sugar beat as the main agricultural crops. A sensitivity analysis indicated that the most significant model parameters were the width of the no-application zone and the degree of plant interception. The simulation was carried out for the 15 most frequently detected substances found in the study area using eight different environmental scenarios, covering variation of the width of the no-application zone, climate, and seasonal scenarios. The highest in-stream concentrations were predicted for a scenario using no (0m) buffer zone in conjunction with increased precipitation. According to the predicted concentrations, the risk for the aquatic communities was estimated based on standard toxicity tests and the application of a safety factor. The simulation results are presented both by means of risk maps for the study area showing the simulated pesticide concentration and the resulting ecological risk for numerous sites under varying scenarios and by case study diagrams with focus on the model behavior under the influence of single parameters. Risk maps confirmed the importance of no-application (buffer) zones for the levels of pesticide input. They also indicated the importance of the existing no-application zones for certain compounds and in some cases the need for a further evaluation of these regulations. The simulation tool was implemented as a standard PC software combining the REXTOX model with a geographical information system and can be used on any current personal computer. All input data was taken from public sources of German authorities. With little effort the tool should be applicable for other areas with similar data quality.

Stream macroinvertebrate drift response to pulsed exposure of the synthetic pyrethroid lambda-cyhalothrin

Outdoor experimental channels were used to study the behavioral changes of stream macroinvertebrates exposed to a pulse of the pyrethroid insecticide lambda-cyhalothrin. The primary end point was the number of macroinvertebrates drifting, but the mobility of macroinvertebrates caught in the drift also was assessed. A specified number of two insect species, Baetis rhodani and Leuctra fusca/digitata, and of the amphipod Gammarus pulex were introduced into small replicated subsections of the experimental channels. Macroinvertebrates were allowed to acclimatize for 26 h prior to a 60-min pulsed exposure to lambda-cyhalothrin. Measurement was initiated 2 h before pesticide application and continued for the following 24 h. Pulse concentrations of lambda-cyhalothrin of 0.001, 0.01, 0.1, and 1.0 microg L(-1) were applied, and each experiment was replicated 8 times. All three species responded to the pesticide pulse with catastrophic drift. The 0.001 microg L(-1) treatment caused a significant increase in the drift of Gammarus, whereas the drift response threshold was 0.01 microg L(-1) for the two insect species. Drift response onset followed the applied pulse concentration, with the highest concentrations resulting in more individuals of all species entering drift at an early stage. The majority of individuals caught in drift samples during low concentrations showed no change in mobility. At the two highest concentrations, however, both Baetis and Leuctra were in the process of being immobilized, with Leuctra the more sensitive of the two. In contrast, only a few of the Gammarus individuals caught showed changes in mobility after the high-concentration treatments. The present study shows that lambda-cyhalothrin is a potential hazard for macroinvertebrate populations in headwater streams. The clear species-specific responses indicate that sublethal doses have the potential to change the macroinvertebrate community structure.

Linking land use variables and invertebrate taxon richness in small and medium-sized agricultural streams on a landscape level

In this study the average numbers of invertebrate species across an arable landscape in central Germany (surveys from 15 years in 90 streams at 202 sites) were assessed for their correlation with environmental factors such as stream width, land use (arable land, forest, pasture, settlement), soil type, and agriculture-derived stressors. The stress originating from arable land was estimated by the factor "risk of runoff," which was derived from a runoff model (rainfall-induced surface runoff). Multivariate analysis explained 39.9% of the variance in species number, revealing stream width as the most important factor (25.3%), followed by risk of runoff (9.7%). The results showed that wider streams--with or without agricultural stressors--contained significantly higher species numbers than narrower streams. This can be explained by potentially more diverse in-stream structures leading to more habitats and niches. However, negative effects on species number owing to runoff from arable land could be distinguished from the effect of stream width: the number of species within each stream width class significantly decreased with increasing risk of runoff. Therefore the factor "risk of runoff" is considered to express a significant proportion of the variability in macroinvertebrate communities caused by stressors of agricultural origin.

Linking in situ bioassays and population dynamics of macroinvertebrates to assess agricultural contamination in streams of the Argentine pampa

The two local crustacean species Hyalella curvispina and Macrobrachium borelli were chosen for assessment of agricultural contamination in two streams (Horqueta and Maguire) in the Argentine pampa. In parallel with in situ bioassays of both species, the population dynamics and the organismic drift of H. curvispina were investigated throughout the main period of insecticide application, from December 2001 to March 2002. In Maguire none of the current-use insecticides (chlorpyrifos, alpha-cypermethrin, and endosulfan) in question were detected throughout the sampling period. During 1-week intervals with no contamination by insecticides the survival rate of H. curvispina varied between 77 +/- 6% (+/- SE, n = 4) and 85 +/- 3%. In Horqueta during a week with a peak insecticide contamination of 64 microg/kg chlorpyrifos in the suspended particles, a mortality of 100% was observed in the in situ bioassays for both species, H. curvispina and M. borelli. At the same time, in Maguire H. curvispina showed reduced survival rates of 23 +/- 5% and 25 +/- 18% at the two sites, while the survival rate of M. borelli was 60 +/- 11% upstream and 93 +/- 5% downstream, below a wetland. During the period with 100% mortality of H. curvispina in Horqueta, the population density of this species decreased correspondingly, from 106 +/- 26 to 0 individuals/m(2). We conclude that in situ bioassays can be successfully linked to in-stream population dynamics for the same species and that this link is very useful for interpreting causal exposure-effect relationships.

Runoff-related agricultural impact in relation to macroinvertebrate communities of the Lourens River, South Africa

A field study at the Lourens River, South Africa, was undertaken during the pesticide application period between November 2001 and January 2002 in order to investigate the potential relation of agricultural pollution to the aquatic macroinvertebrate fauna. The upper regions of the Lourens River were free of contamination (LR1), whereas subsequent stretches flowing through a 400-ha orchard area (LR2) received transient insecticide peaks. Continuously operating suspended-particle samplers as well as flood samplers operating during runoff events were used to measure pesticide contamination. In addition, various physicochemical and morphological parameters were examined. A survey of the macroinvertebrate communities associated with the rocky substrates was carried out every three weeks. Community indices were calculated using the South African Scoring System (SASS 5) for bioassessment of water quality in rivers. The two sites differed in pesticide pollution as well as in average turbidity levels (LR1 5.5 mg/L; LR2 64.3 mg/L), but were similar in bottom substrate composition and most other abiotic factors. At the downstream site (LR2), pesticide values of 0.05 microg/L azinphos-methyl in water as well as 49 microg/kg azinphos-methyl, 94 microg/kg chlorpyrifos and 122 microg/kg total endosulfan in suspended particles were found during runoff conditions. The macroinvertebrate communities of the two sampling sites were similar in terms of number of total individuals, but differed significantly (ANOVA) in average number of taxa (LR1 11.7, LR2 8.9). Seven out of 17 investigated taxa occurred in significantly reduced numbers or were even absent at the downstream site LR2. The community characteristics determined by SASS 5 showed a significantly less sensitive community structure at the downstream site (TS 41; ASPT 4.6), indicating continuously lower water quality compared to site LR1 (TS 80; ASPT 6.9). It is concluded that the Lourens River macroinvertebrate communities are affected by agricultural pollution, with pesticides and increased turbidity as the most important stressors.

Field studies on exposure, effects, and risk mitigation of aquatic nonpoint-source insecticide pollution: a review

Recently, much attention has been focused on insecticides as a group of chemicals combining high toxicity to invertebrates and fishes with low application rates, which complicates detection in the field. Assessment of these chemicals is greatly facilitated by the description and understanding of exposure, resulting biological effects, and risk mitigation strategies in natural surface waters under field conditions due to normal farming practice. More than 60 reports of insecticide-compound detection in surface waters due to agricultural nonpoint-source pollution have been published in the open literature during the past 20 years, about one-third of them having been undertaken in the past 3.5 years. Recent reports tend to concentrate on specific routes of pesticide entry, such as runoff, but there are very few studies on spray drift-borne contamination. Reported aqueous-phase insecticide concentrations are negatively correlated with the catchment size and all concentrations of > 10 microg/L (19 out of 133) were found in smaller-scale catchments (< 100 km2). Field studies on effects of insecticide contamination often lack appropriate exposure characterization. About 15 of the 42 effect studies reviewed here revealed a clear relationship between quantified, non-experimental exposure and observed effects in situ, on abundance, drift, community structure, or dynamics. Azinphos-methyl, chlorpyrifos, and endosulfan were frequently detected at levels above those reported to reveal effects in the field; however, knowledge about effects of insecticides in the field is still sparse. Following a short overview of various risk mitigation or best management practices, constructed wetlands and vegetated ditches are described as a risk mitigation strategy that have only recently been established for agricultural insecticides. Although only 11 studies are available, the results in terms of pesticide retention and toxicity reduction are very promising. Based on the reviewed literature, recommendations are made for future research activities.