Jes J. Rasmussen

Thresholds for the Effects of Pesticides on Invertebrate Communities and Leaf Breakdown in Stream Ecosystems

We compiled data from eight field studies conducted between 1998 and 2010 in Europe, Siberia, and Australia to derive thresholds for the effects of pesticides on macroinvertebrate communities and the ecosystem function leaf breakdown. Dose-response models for the relationship of pesticide toxicity with the abundance of sensitive macroinvertebrate taxa showed significant differences to reference sites at 1/1000 to 1/10,000 of the median acute effect concentration (EC50) for Daphnia magna, depending on the model specification and whether forested upstream sections were present. Hence, the analysis revealed effects well below the threshold of 1/100 of the EC50 for D. magna incorporated in the European Union Uniform Principles (UP) for registration of single pesticides. Moreover, the abundances of sensitive macroinvertebrates in the communities were reduced by 27% to 61% at concentrations related to 1/100 of the EC50 for D. magna. The invertebrate leaf breakdown rate was positively linearly related to the abundance of pesticide-sensitive macroinvertebrate species in the communities, though only for two of the three countries examined. We argue that the low effect thresholds observed were not mainly because of an underestimation of field exposure or confounding factors. From the results gathered we derive that the UP threshold for single pesticides based on D. magna is not protective for field communities subject to multiple stressors, pesticide mixtures, and repeated exposures and that risk mitigation measures, such as forested landscape patches, can alleviate effects of pesticides.

Stream habitat structure influences macroinvertebrate response to pesticides

Agricultural pesticides continue to impair surface water ecosystems, although there are few assessments of interactions with other modifications such as fine sediment and physical alteration for flood drainage. We, therefore, surveyed pesticide contamination and macroinvertebrates in 14 streams along a gradient of expected pesticide exposure using a paired-reach approach to differentiate effects between physically modified and less modified sites. Apparent pesticides effects on the relative abundance of SPEcies At Risk (SPEAR) were increased at sites with degraded habitats primarily due to the absence of species with specific preferences for hard substrates. Our findings highlight the importance of physical habitat degradation in the assessment and mitigation of pesticide risk in agricultural streams.

Integrated assessment of the impact of chemical stressors on surface water ecosystems.

The release of chemicals such as chlorinated solvents, pesticides and other xenobiotic organic compounds to streams, either from contaminated sites, accidental or direct application/release, is a significant threat to water resources. In this paper, different methods for evaluating the impacts of chemical stressors on stream ecosystems are evaluated for a stream in Denmark where the effects of major physical habitat degradation can be disregarded. The methods are: (i) the Danish Stream Fauna Index, (ii) Toxic Units (TU), (iii) SPEAR indices, (iv) Hazard Quotient (HQ) index and (v) AQUATOX, an ecological model. The results showed that the hydromorphology, nutrients, biological oxygen demand and contaminants (pesticides and trichloroethylene from a contaminated site) originating from groundwater do not affect the good ecological status in the stream. In contrast, the evaluation by the novel SPEAR(pesticides) index and TU indicated that the site is far from obtaining good ecological status - a direct contradiction to the ecological index currently in use in Denmark today - most likely due to stream sediment-bound pesticides arising from the spring spraying season. In order to generalise the findings of this case study, the HQ index and AQUATOX were extended for additional compounds, not only partly to identify potential compounds of concern, but also to determine thresholds where ecological impacts could be expected to occur. The results demonstrate that some commonly used methods for the assessment of ecological impact are not sufficient for capturing - and ideally separating - the effects of all anthropogenic stressors affecting ecosystems. Predictive modelling techniques can be especially useful in supporting early decisions on prioritising hot spots, serving to identify knowledge gaps and thereby direct future data collection. This case study presents a strong argument for combining bioassessment and modelling techniques to multi-stressor field sites, especially before cost-intensive studies are conducted.

The legacy of pesticide pollution: An overlooked factor in current risk assessments of freshwater systems

We revealed a history of legacy pesticides in water and sediment samples from 19 small streams across an agricultural landscape. Dominant legacy compounds included organochlorine pesticides, such as DDT and lindane, the organophosphate chlorpyrifos and triazine herbicides such as terbutylazine and simazine which have long been banned in the EU. The highest concentrations of legacy pesticides were found in streams draining catchments with a large proportion of arable farmland suggesting that they originated from past agricultural applications. The sum of toxic units (SumTUD.magna) based on storm water samples from agriculturally impacted streams was significantly higher when legacy pesticides were included compared to when they were omitted. Legacy pesticides did not significantly change the predicted toxicity of water samples to algae or fish. However, pesticide concentrations in bed sediment and suspended sediment samples exceeded safety thresholds in 50% of the samples and the average contribution of legacy pesticides to the SumTUC.riparius was >90%. Our results suggest that legacy pesticides can be highly significant contributors to the current toxic exposure of stream biota, especially macroinvertebrate communities, and that those communities were primarily exposed to legacy pesticides via the sediment. Additionally, our results suggest that neglecting legacy pesticides in the risk assessment of pesticides in streams may severely underestimate the risk of ecological effects.

Sources, occurrence and predicted aquatic impact of legacy and contemporary pesticides in streams

We couple current findings of pesticides in surface and groundwater to the history of pesticide usage, focusing on the potential contribution of legacy pesticides to the predicted ecotoxicological impact on benthic macroinvertebrates in headwater streams. Results suggest that groundwater, in addition to precipitation and surface runoff, is an important source of pesticides (particularly legacy herbicides) entering surface water. In addition to current-use active ingredients, legacy pesticides, metabolites and impurities are important for explaining the estimated total toxicity attributable to pesticides. Sediment-bound insecticides were identified as the primary source for predicted ecotoxicity. Our results support recent studies indicating that highly sorbing chemicals contribute and even drive impacts on aquatic ecosystems. They further indicate that groundwater contaminated by legacy and contemporary pesticides may impact adjoining streams. Stream observations of soluble and sediment-bound pesticides are valuable for understanding the long-term fate of pesticides in aquifers, and should be included in stream monitoring programs.

How to Characterize Chemical Exposure to Predict Ecologic Effects on Aquatic Communities

Reliable characterization of exposure is indispensable for ecological risk assessment of chemicals. To deal with mixtures, several approaches have been developed, but their relevance for predicting ecological effects on communities in the field has not been elucidated. In the present study, we compared nine metrics designed for estimating the total toxicity of mixtures regarding their relationship with an effect metric for stream macroinvertebrates. This was done using monitoring data of biota and organic chemicals, mainly pesticides, from five studies comprising 102 streams in several regions of Europe and South-East Australia. Mixtures of less than 10 pesticides per water sample were most common for concurrent exposure. Exposure metrics based on the 5% fraction of a species sensitivity distribution performed best, closely followed by metrics based on the most sensitive species and Daphnia magna as benchmark. Considering only the compound with the highest toxicity and ignoring mixture toxicity was sufficient to estimate toxicity in predominantly agricultural regions with pesticide exposure. The multisubstance Potentially Affected Fraction (msPAF) that combines concentration and response addition was advantageous in the study where further organic toxicants occurred. We give recommendations on exposure metric selection depending on data availability and the involved compounds.

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.

Effects of a triazole fungicide and a pyrethroid insecticide on the decomposition of leaves in the presence or absence of macroinvertebrate shredders

Previously, laboratory experiments have revealed that freely diluted azole fungicides potentiate the direct toxic effect of pyrethroid insecticides on Daphnia magna. More ecologically relevant exposure scenarios where pesticides are adsorbed have not been addressed. In this study we exposed beech leaves (Fagus sylvatica) to the azole fungicide propiconazole (50 or 500 μg L(-1)), the pyrethroid insecticide alpha-cypermethrin (0.1 or 1 μg L(-1)) or any combination of the two for 3h. Exposed leaves were transferred to aquaria with or without an assemblage of macroinvertebrate shredders, and we studied treatment effects on rates of microbial leaf decomposition, microbial biomass (using C:N ratio as a surrogate measure) and macroinvertebrate shredding activity during 26 days post-exposure. Microbial leaf decomposition rates were significantly reduced in the propiconazole treatments, and the reduction in microbial activity was significantly correlated with loss of microbial biomass (increased C:N ratio). Macroinvertebrate shredding activity was significantly reduced in the alpha-cypermethrin treatments. In addition, the macroinvertebrate assemblage responded to the propiconazole treatments by increasing their consumption of leaf litter with lower microbial biomass, probably to compensate for the reduced nutritional quality of this leaf litter. We found no interaction between the two pesticides on macroinvertebrate shredding activity, using Independent Action as a reference model. In terms of microbial leaf decomposition rates, however, alpha-cypermethrin acted as an antagonist on propiconazole. Based on these results we emphasise the importance of considering indirect effects of pesticides in the risk assessment of surface water ecosystems.

A catchment scale evaluation of multiple stressor effects in headwater streams.

Mitigation activities to improve water quality and quantity in streams as well as stream management and restoration efforts are conducted in the European Union aiming to improve the chemical, physical and ecological status of streams. Headwater streams are often characterised by impairment of hydromorphological, chemical, and ecological conditions due to multiple anthropogenic impacts. However, they are generally disregarded as water bodies for mitigation activities in the European Water Framework Directive despite their importance for supporting a higher ecological quality in higher order streams. We studied 11 headwater streams in the Hove catchment in the Copenhagen region. All sites had substantial physical habitat and water quality impairments due to anthropogenic influence (intensive agriculture, urban settlements, contaminated sites and low base-flow due to water abstraction activities in the catchment). We aimed to identify the dominating anthropogenic stressors at the catchment scale causing ecological impairment of benthic macroinvertebrate communities and provide a rank-order of importance that could help in prioritising mitigation activities. We identified numerous chemical and hydromorphological impacts of which several were probably causing major ecological impairments, but we were unable to provide a robust rank-ordering of importance suggesting that targeted mitigation efforts on single anthropogenic stressors in the catchment are unlikely to have substantial effects on the ecological quality in these streams. The SPEcies At Risk (SPEAR) index explained most of the variability in the macroinvertebrate community structure, and notably, SPEAR index scores were often very low (<10% SPEAR abundance). An extensive re-sampling of a subset of the streams provided evidence that especially insecticides were probably essential contributors to the overall ecological impairment of these streams. Our results suggest that headwater streams should be considered in future management and mitigation plans. Catchment-based management is necessary because several anthropogenic stressors exceeded problematic thresholds, suggesting that more holistic approaches should be preferred.

Networking our way to better ecosystem service provision

The ecosystem services (EcoS) concept is being used increasingly to attach values to natural systems and the multiple benefits they provide to human societies. Ecosystem processes or functions only become EcoS if they are shown to have social and/or economic value. This should assure an explicit connection between the natural and social sciences, but EcoS approaches have been criticized for retaining little natural science. Preserving the natural, ecological science context within EcoS research is challenging because the multiple disciplines involved have very different traditions and vocabularies (common-language challenge) and span many organizational levels and temporal and spatial scales (scale challenge) that define the relevant interacting entities (interaction challenge). We propose a network-based approach to transcend these discipline challenges and place the natural science context at the heart of EcoS research.