Use of vegetated agricultural drainage ditches to decrease toxicity of irrigation runoff from tomato and alfalfa fields in California, USA

Potential of vegetated ditches to manage organic pollutants derived from agricultural runoff and domestic sewage: A case study in Sinaloa (Mexico)

This case study presents the fate of selected organic, priority and emerging pollutants along a 3.6km sector of a vegetated, agricultural ditch situated in Sinaloa (Mexico). The ditch receives runoff of agriculture and domestic wastewater from an adjacent community. During 2013, the occurrence of 38 organic pollutants (pesticides, polycyclic aromatic hydrocarbons (PAHs), artificial sweeteners and pharmaceutical residues) was monitored monthly at five selected points in the ditch water. Additionally, sediment and Typha domingensis (cattail) plants were collected in March, June, and September 2013 and investigated concerning their ability to absorb and accumulate pollutants. The concentrations of the selected pollutants in the ditch water ranged from sub ngL^-1 (metolachlor, atrazine) to μgL^-1 (metalaxyl, acesulfame). The metabolites endosulfan sulfate and endosulfan lactone exceeded mostly the concentration of the precursor insecticide endosulfan. Sorption on sediments was of minor relevance for accumulation of pollutants in the ditch system. Concentrations in the sediments varied seasonally and ranged from 0.2 to 12,432μgkg^-1 dry weight (d.w.). T. domingensis accumulated ten of the studied pollutants mainly in roots (5-1065μgkg^-1 d.w.). Overall, the monitoring results of the ditch compartments indicated that downstream the concentrations of the target pollutants decreased. Under no-flow conditions in the hot season, the ditch revealed a noticeable potential to mitigate pollutants. Among the high microbial activity in the water and the subtropical climate conditions, the ditch vegetation contributed to natural attenuation of the selected pollutants.

Do Varying Aquatic Plant Species Affect Phytoplankton and Crustacean Responses to a Nitrogen-Permethrin Mixture?

Hydraulically connected wetland microcosms vegetated with either Typha latifolia or Myriophyllum aquaticum were amended with an NH₄NO₃ and permethrin mixture to assess the effectiveness of both plant species in mitigating effects of the pollutant mixture on phytoplankton (as chlorophyll a) and Hyalella azteca. Phytoplankton grew in response to increased NH₄NO₃ in the presence of all plant species, but was unaffected by exposure to permethrin. H. azteca responses occurred rapidly (0.17 days), was mitigated within 1-2 days, and aqueous toxicity was unaffected by plant species type. A toxic unit model approach ascertained primary toxicity was permethrin with minimal additional toxicity from NH₄NO₃. Varying aquatic plant species had only modest influences on phytoplankton responses and no observable influence on animal responses during nitrogen-permethrin mixture exposures. As a result, both T. latifolia and M. aquaticum can be used as part of an effective agricultural best-management practice system for mitigating pollutant impacts of agricultural run-off.

Variability of glyphosate and diuron sorption capacities of ditch beds determined using new indicator-based methods

Pesticide sorption to ditch-bed materials can efficiently decrease pesticide concentrations in the flowing water. Pesticide sorption depends on flood characteristics and the nature and abundance of ditch-bed materials, such as soils, living and decaying vegetation and ash. However, the affinities of pesticides for various ditch-bed materials have rarely been investigated, and variations in the global sorption capacity of ditch beds resulting from their heterogeneous compositions and variable flood characteristics have not been determined. Thus, we studied the variability of sorption capacities of ditch-bed materials for glyphosate and diuron in three catchments in France and propose a method for calculating global sorption processes in heterogeneous ditch beds. The methodology consists in estimating a global sorption coefficient for the composite ditch-bed materials (Kdditch) and an indicator of the amount of pesticide potentially retained by sorption during a flood event (SPRI). Furthermore, we computed the Kdditch and SPRI of glyphosate and diuron for 8 ditches subjected to 3h flood events with water levels varying from 0.5 to 15cm. Our results show that increasing the water level from 0.5 to 15cm resulted in a 90% decrease in the sorption capacities of the ditch beds for both pesticides. At a medium water depth of 5cm, SPRI varied from 25 to 51% and from 7 to 35% among the ditches for glyphosate and diuron, respectively. The variabilities of the glyphosate and diuron sorption capacities among the ditches were mainly driven by the nature and abundance of soil and ash. As the management of farm ditches, performed to maintain their hydraulic performance, modifies the abundances of various ditch-bed materials, it constitutes a potential lever of action for water quality improvement. Thus, Kdditch and SPRI could serve as rapid and cost-effective tools for optimizing ditch network management strategies to improve water quality in cropped catchments.

Evaluation of pesticide monitoring strategies in agricultural streams based on the toxic-unit concept--experiences from long-term measurements

The European Water Framework Directive requires surface water bodies to have a good chemical and ecological status. Although relatively few pesticides are included in the list of priority pollutants, they pose, due to their intrinsic biological activity, a significant risk for the integrity of aquatic ecosystems. In this context, the pesticide (up to 128 pesticides including some transformation products) exposure pattern in four agricultural streams and two rivers was determined from 2002 to 2011 under the umbrella of the Swedish national monitoring program employing time-proportional and grab sampling strategies, respectively. After transforming the measured pesticide concentrations into toxic units, the European Uniform Principles for algae (chronic), invertebrates and fish (both acute), which are partly employed as benchmark for pesticide regulation, were only occasionally (<2%) exceeded. Moreover, this evaluation showed no long-term trends over the years. However, recent publications suggested that those thresholds are not protective for ecosystem structure and function, indicating a risk of up to 20% and 35% of the samples from the agricultural streams and the rivers, respectively. Moreover, the monitoring data show a continuous but rather low toxic potential of pesticides for all three trophic levels throughout the year, which suggests pesticides as an evolutionary force in agriculturally impacted aquatic ecosystems. However, the flow-triggered sampling, which was implemented as an additional sampling strategy in one of the agricultural streams starting in 2006, displayed an up to 7-fold underestimation of the maximum concentration in terms of toxic units for daphnids and fish during run-off events. The present study thus underpins that the optimal sampling design for pesticide monitoring strongly depends on its overall purpose. If the long-term exposure pattern is of concern a time-proportional composite sampling strategy is recommended, while for an assessment of peak exposures a flow-event-triggered high-resolution sampling strategy is superior.

Application of a redox gradostat reactor for assessing rhizosphere microorganism activity on lambda-cyhalothrin

Bacterial activity on pesticides can lead to decreased toxicity or persistence in aquatic systems. Rhizosphere activity is difficult to measure in situ. To mimic rhizosphere properties of the soft rush, Juncus effusus, a single-stage gradostat reactor was developed to study cycling of lambda-cyhalothrin by rhizobacteria and the effects of Fe(III) and citrate, both common in wetland soil, on lambda-cyhalothrin degradation. Redox gradient changes, greater than ± 10 mV, were apparent within days 5-15 both in the presence and absence of ferric citrate. Through the production of a redox gradient (p < 0.05) by rhizobacteria and the ability to measure pesticide loss over time (p < 0.05), reactors were useful in expanding knowledge on this active environment.

Effects of peak exposure scenarios on Gammarus fossarum using field relevant pesticide mixtures

The present study investigated sublethal effects of a field relevant pesticide mixture (one herbicide, three fungicides, five insecticides) on Gammarus fossarum by considering different peak exposure scenarios, which may be generated by the inherent properties of vegetated ditches. Additional experiments aimed at the identification of germane exposure pathways (food and water). Therefore, G. fossarum were exposed in independent experiments to three scenarios, which differed besides in the peak concentration of the pesticide mixture also in the mixture's composition and exposure duration (n=20 per treatment). The exposure duration of 12 or 120 min was followed by a seven-day post-exposure observation period. At a constant concentration-time product, a lower exposure duration in concert with a proportionally higher peak concentration caused a substantially elevated ecotoxicity compared to a treatment with a longer exposure duration at a lower peak concentration. Given the importance of the insecticide lambda-cyhalothrin for the mixture's ecotoxicity it may be concluded that the fast mode of action of pyrethroids mainly explains this observation. Moreover, field relevant concentrations of the pesticide mixture applied at an exposure duration of 120 min resulted in reduced gammarids' feeding rate, which may be indicative for shifts in the ecosystem function of leaf litter breakdown and hence the provision of energy for local and downstream communities. Finally, the present study indicated that both pathways of exposure, namely via food or water, reduce gammarids' feeding rate synergistically. This suggests that both exposure pathways should be considered for compounds exhibiting a high Kow (e.g. pyrethroids) during the risk assessment of single substances and mixtures.

Mitigation of malathion's acute toxicity by four submersed macrophyte species

Some submersed macrophyte species rapidly sorb some insecticides from the water, potentially reducing exposure for aquatic species. The rates at which macrophytes remove insecticides, however, can differ widely among plant species. Furthermore, few studies have examined how much macrophytes actually influence insecticide toxicity to sensitive animals. The authors quantified the ability of several macrophyte species to mitigate insecticide toxicity by comparing the survival of the aquatic herbivore, Daphnia magna, following exposure to a factorial combination of 3 malathion concentrations (0 µg/L, 3 µg/L, and 24 µg/L) and 7 macrophyte treatments (no macrophytes, 4 different macrophyte monocultures, and 2 inert substrates: plastic plants and polypropylene rope). The authors also quantified the rate that different macrophytes reduced malathion's toxicity by exposing D. magna to water samples collected from each treatment after 2 h, 8 h, and 48 h of exposure. The results revealed that whereas 3 µg/L and 24 µg/L of malathion decimated D. magna in the no-macrophyte, plastic plant, and rope treatments, all 4 macrophyte species strongly mitigated these effects. When the authors compared the rate at which malathion's toxicity decreased, they found that all macrophytes negated malathion's toxicity within 2 h, whereas it took more than 8 h in the absence of macrophytes or in the presence of inert substrates. These results demonstrate that numerous macrophyte species can equally and strongly mitigate insecticide toxicity, whereas inert substrates cannot.

Effect-based tools for monitoring and predicting the ecotoxicological effects of chemicals in the aquatic environment

Ecotoxicology faces the challenge of assessing and predicting the effects of an increasing number of chemical stressors on aquatic species and ecosystems. Herein we review currently applied tools in ecological risk assessment, combining information on exposure with expected biological effects or environmental water quality standards; currently applied effect-based tools are presented based on whether exposure occurs in a controlled laboratory environment or in the field. With increasing ecological relevance the reproducibility, specificity and thus suitability for standardisation of methods tends to diminish. We discuss the use of biomarkers in ecotoxicology including ecotoxicogenomics-based endpoints, which are becoming increasingly important for the detection of sublethal effects. Carefully selected sets of biomarkers allow an assessment of exposure to and effects of toxic chemicals, as well as the health status of organisms and, when combined with chemical analysis, identification of toxicant(s). The promising concept of “adverse outcome pathways (AOP)” links mechanistic responses on the cellular level with whole organism, population, community and potentially ecosystem effects and services. For most toxic mechanisms, however, practical application of AOPs will require more information and the identification of key links between responses, as well as key indicators, at different levels of biological organization, ecosystem functioning and ecosystem services.

Changes in gene transcription and whole organism responses in larval fathead minnow (Pimephales promelas) following short-term exposure to the synthetic pyrethroid bifenthrin

The combination of molecular and whole-organism endpoints in ecotoxicology provides valuable information about the ecological relevance of sublethal stressor effects in aquatic ecosystems such as those caused by the use of insecticides and translocation of their residues into surface waters. This study contributes knowledge about the sublethal effects of a common use insecticide, the synthetic pyrethroid bifenthrin, on larval fathead minnow (Pimephales promelas). Transcriptomic responses, assessed by quantitative real-time PCR, combined with individual effects on swimming performance were used to estimate the ecological relevance of insecticide impacts. Significant transcriptomic responses were observed at 0.07 μg L(-1) bifenthrin (lowest observed effect concentration, LOEC) but mostly followed a biphasic rather than a linear dose-response with increasing concentration. Transcript patterns for genes involved in detoxification, neuromuscular function and energy metabolism were linked to an impairment of swimming performance at ≥0.14 μg L(-1) bifenthrin. With increasing treatment concentration, a significant down-regulation was observed for genes coding for cyp3a, aspartoacylase, and creatine kinase, whereas metallothionein was up-regulated. Additionally, bifenthrin induced endocrine responses as evident from a significant up-regulation of vitellogenin and down-regulation of insuline-like growth factor transcripts. Recovery occurred after 6 days and was dependent on the magnitude of the initial stress. During the recovery period, down-regulation of vitellogenin was observed at lowest exposure concentrations. The data presented here emphasize that links can be made between gene transcription changes and behavioral responses which is of great value for the evaluation and interpretation of biomarker responses.