Spray deposition of two insecticides into surface waters in a South African orchard area

Assessing Effects of Genetically Modified Plant Material on the Aquatic Environment Using higher-tier Studies

Genetically modified organisms are used extensively in agriculture. To assess potential side effects of genetically modified (GM) plant material on aquatic ecosystems, only a very small number of higher-tier studies have been performed. At the same time, these studies are particularly important for comprehensive risk assessment covering complex ecological relationships. Here we evaluate the methods of experimental higher-tier effect studies with GM plant material (or Bt toxin) in comparison to those well-established for pesticides. A major difference is that nominal test concentrations and thus dose-response relationships cannot easily be produced with GM plant material. Another important difference, particularly to non-systemic pesticides, is that aquatic organisms are exposed to GM plant material primarily through their feed. These and further differences in test requirements, compared with pesticides, call for a standardisation for GM-specific higher-tier study designs to assess their potentially complex effects in the aquatic ecosystems comprehensively.

Organophosphate pesticides in South African eutrophic estuaries: Spatial distribution, seasonal variation, and ecological risk assessment

The seasonal variation, spatial distribution, and ecological risks of thirteen organophosphate pesticides (OPPs) were studied in the Sundays and Swartkops estuaries in South Africa. Ten pesticides were detected in surface water samples from both estuaries, while all OPPs were detected in sediments. The highest concentration of OPPs (18.8 μg pyrazophos L^-1) was detected in surface water samples from Swartkops Estuary, while 48.7 μg phosalone kg^-1 dw was the highest in sediments collected from Sundays Estuary. There was no clear seasonal pattern in OPPs occurrence in surface water from both systems. However, their occurrence in sediments was in the following order: winter > autumn > summer > spring, perhaps indicating major pesticide input in the winter seasons. Results from ecological risk assessment showed that pyraclofos and chlorpyrifos (CHL) in surface water from both systems are respectively likely to cause high acute and chronic toxicity to fish (risk quotient - RQ > 1). For sediments of both estuaries, the highest acute and chronic RQs for fish were calculated for isazophos and CHL respectively. The majority of the detected OPPs in sediments posed potential high risks to Daphnia magna from both systems. These results suggest that these aquatic organisms (fish, and Daphnia), if present in the studied estuaries, can develop certain forms of abnormalities due to OPP exposure. To this end, proper measures should be taken to reduce OPP input into the estuarine systems.

Characterizing the exposure of streams in southern Ontario to agricultural pesticides

Aquatic communities can be exposed to pesticides transported from land. Characterizing this exposure is key to predicting potential toxic effects. In this study, samples of streamwater from 21 sites were used to characterize pesticide exposure to aquatic communities. Sites were in agricultural areas of southwestern Ontario, Canada and were sampled monthly from 2012 to 2019 from April to November. Samples were analyzed for a suite of hundreds of pesticides and pesticide degradation products and other water quality indicators (e.g., nutrients). Frequently detected pesticides included herbicides (2,4-D; bentazon; MCPP; metolachlor) and neonicotinoid insecticides (NNIs) (clothianidin; thiamethoxam) which were detected in >50% of samples collected between 2015 and 2019. Non-metric multidimensional scaling (NMDS) was used to explore connections between pesticide concentrations and upstream land use and crop type. Detectable concentrations of the NNI clothianidin and many herbicides were related to corn, soybean, and grain/cereal crops while concentrations of the NNI imidacloprid, insecticide flonicamid, and fungicide boscalid were related to greenhouse/nursery land use. Potential toxicity to aquatic communities was assessed by comparing pesticide concentrations to Pesticide Toxicity Index (PTI) values. Few samples exceeded levels where acute (1% of samples) or chronic toxicity (10.5%) would be expected. The diamide insecticide chlorantraniliprole was detected in several streamwater samples at levels that may cause toxicity to aquatic invertebrates, highlighting the need for continued toxicity research into this pesticide class. The number of pesticides detected was positively correlated with nutrient and total suspended solids levels, underscoring the multiple stressors aquatic communities are exposed to in these habitats.

Organophosphate pesticides sequestered in tissues of a seagrass species - Zostera capensis from a polluted watershed

Organophosphate pesticides (OPPs) are persistent in the environment, but little information is available on their bioaccumulation in seagrass. In this study, the seagrass - Zostera capensis was collected from Swartkops Estuary in South Africa to investigate the bioaccumulation of OPPs from contaminated sediments and the water column. This plant was chosen because it grows abundantly in the estuary's intertidal zone, making it a viable phytoremediator in the urban environment. Extraction was performed by the QuEChERS method followed by GC-MS analysis. The mean concentration of ∑OPPs ranged from 0.01 to 0.03 μg/L for surface water; 6.20-13.35 μg/kg dw for deep-rooted sediments; 18.79-37.75 μg/kg dw for leaf tissues and 12.14-39.80 μg/kg dw for root tissues of Z. capensis. The biota-sediment accumulation factors (BSAFs) were greater than one, indicating the potential for Z. capensis to bioaccumulate and intercept the targeted pesticides. A weak insignificant correlation observed between log BSAFs and log Kow indicates that the bioaccumulation of OPPs in tissues of Z. capensis were not dependent on the Kow. Eight of the selected pesticides had root-leaf translocation factors (TFr-l) greater than 1, indicating that Z. capensis can transport these chemicals from roots to leaves. The results from this study implies that this plant species can clean up OPP contamination in the environment.

The effect of dimethoate pesticide on some biochemical biomarkers in Gammarus pulex

In this presented study, it was aimed to determine the effects of pesticides on non-target organisms on the freshwater amphipod, Gammarus pulex, by biochemical responses. Acute toxicity value (LC₅₀) in G. pulex of the dimethoate pesticide was determined. The superoxide dismutase (SOD), glutathione S-transferaz (GST), glutathione peroxidase (GPx), and catalase (CAT) activities and malondialdehyde (MDA), glutathione (GSH) levels of the G. pulex organism exposed to the subletal concentrations were analyzed by ELISA for 24 and 96 h. In conclusion, the present study demonstrated the abilities of dimethoate pesticide induce to oxidative stress. The results revealed that MDA, GSH levels SOD, CAT, GPx, and GST activities of G. pulex can be used as an effective biomarkers.

Evaluation of Watershed-Scale Simulations of In-Stream Pesticide Concentrations from Off-Target Spray Drift

The estimation of pesticide concentrations in surface water bodies is a critical component of the environmental risk assessment process required by regulatory agencies in North America, the European Union, and elsewhere. Pesticide transport to surface waters via deposition from off-field spray drift can be an important route of potential contamination. The spatial orientation of treated fields relative to receiving water bodies make prediction of off-target pesticide spray drift deposition and resulting aquatic estimated environmental concentrations (EECs) challenging at the watershed scale. The variability in wind conditions further complicates the simulation of the environmental processes leading to pesticide spray drift contributions to surface water. This study investigates the use of the Soil Water Assessment Tool (SWAT) for predicting concentrations of malathion (O,O-deimethyl thiophosphate of diethyl mercaptosuccinate) in a flowing water body when exposure is a result of off-target spray drift, and assesses the model's performance using a parameterization typical of a screening-level regulatory assessment. Six SWAT parameterizations, each including incrementally more site-specific data, are then evaluated to quantify changes in model performance. Results indicate that the SWAT model is an appropriate tool for simulating watershed scale concentrations of pesticides resulting from off-target spray drift deposition. The model predictions are significantly more accurate when the inputs and assumptions accurately reflect application practices and environmental conditions. Inclusion of detailed wind data had the most significant impact on improving model-predicted EECs in comparison to observed concentrations.

Ecotoxicity of 1,3-dichloropropene, metam sodium, and dazomet on the earthworm Eisenia fetida with modified artificial soil test and natural soil test

1,3-Dichloropropene (1,3-D), metam sodium (MS), and dazomet (DZ) are widely used as preplant soil fumigants to solve soilborne problems. To provide a more scientific and accurate evaluation of 1,3-D, MS, and DZ toxicity to the earthworm Eisenia fetida, modified artificial soil test and natural soil test were studied. The suitable soil moisture to maintain over 90% survival of the earthworms after 4 weeks of treatment in an enclosed system for modified artificial soil test and natural soil test were 26.9 to 86.4% of water-holding capacity (WHC) and 66.2 to 84.3% of WHC, respectively. The optimal soil moisture levels for modified artificial soil test and natural soil test (75 and 55% of WHC, respectively) were finally used to evaluate the toxicity of 1,3-D, MS, and DZ on earthworms. Each desiccator with 10 earthworms and natural or artificial soil was stored at 20 ± 1 °C under constant light of 400 to 800 lx for 2 weeks. The modified artificial soil test showed LC₅₀ values for 1,3-D, MS, and DZ of 3.60, 1.69, and 5.41 mg a.i. kg^-1 soil, respectively. The modified natural soil test of the fumigants showed similar LC₅₀ values of 2.77 and 0.65 mg a.i. kg^-1 soil, except for DZ at 0.98 mg a.i. kg^-1 soil. The present study confirms that both modified artificial soil test and modified natural soil test offer standard methods for acute toxicity test of 1,3-D, MS, and DZ on the earthworms and scientific evidences for assessing the effects of soil fumigants on non-target organisms in the soils. Graphical Abstract Two novel acute toxicity test methods for soil fumigants on the earthworm Eisenia fetida.

Interactive effects of ultraviolet-B radiation and pesticide exposure on DNA photo-adduct accumulation and expression of DNA damage and repair genes in Xenopus laevis embryos

Pesticide use and ultraviolet-B (UVB) radiation have both been suggested to adversely affect amphibians; however, little is known about their interactive effects. One potential adverse interaction could involve pesticide-induced dysregulation of DNA repair pathways, resulting in greater numbers of DNA photo-adducts from UVB exposure. In the present study, we investigated the interactive effects of UVB radiation and two common pesticides (endosulfan and α-cypermethrin) on induction of DNA photo-adducts and expression of DNA damage and repair related genes in African clawed frog (Xenopus laevis) embryos. We examined 13 genes that are, collectively, involved in stress defense, cell cycle arrest, nucleotide excision repair (NER), base excision repair, mismatch repair, DNA repair regulation, and apoptosis. We exposed X. laevis embryos to 0, 25, and 50 μg/L endosulfan or 0, 2.5, and 5.0 μg/L α-cypermethrin for 96 h, with environmentally relevant exposures of UVB radiation during the last 7 h of the 96 h exposure. We measured the amount of cyclobutane pyrimidine dimers (CPDs) and mRNA abundance of the 13 genes among treatments including control, pesticide only, UVB only, and UVB and pesticide co-exposures. Each of the co-exposure scenarios resulted in elevated CPD levels compared to UVB exposure alone, suggesting an inhibitory effect of endosulfan and α-cypermethrin on CPD repair. This is attributed to results indicating that α-cypermethrin and endosulfan reduced mRNA abundance of XPA and HR23B, respectively, to levels that may affect the initial recognition of DNA lesions. In contrast, both pesticides increased transcript abundance of CSA and MUTL. In addition, mRNA abundance of HSP70 and GADD45α were increased by endosulfan and mRNA abundance of XPG was increased by α-cypermethrin. XPC, HR23B, XPG, and GADD45α exhibited elevated mRNA concentrations whereas there was a reduction in MUTL transcript concentrations in UVB-alone treatments. It appeared that even though expression of XPC and CSA were induced by exposure to UVB or pesticides, XPA was the limiting factor in the NER pathway. Our results suggest that pesticides may increase the accumulation of UVB-induced DNA photo-adducts and one likely mechanism is the alteration of critical NER gene expression. The present study provides important implications for evaluating the combined risks of pesticide usage and potentially increasing UVB radiation in aquatic ecosystems.

Development and field validation of an indicator to assess the relative mobility and risk of pesticides in the Lourens River catchment, South Africa

A GIS based pesticide risk indicator that integrates exposure variables (i.e. pesticide application, geographic, physicochemical and crop data) and toxicity endpoints (using species sensitivity distributions) was developed to estimate the Predicted Relative Exposure (PREX) and Predicted Relative Risk (PRRI) of applied pesticides to aquatic ecosystem health in the Lourens River catchment, Western Cape, South Africa. Samples were collected weekly at five sites from the beginning of the spraying season (October) till the beginning of the rainy season (April) and were semi quantitatively analysed for relevant pesticides applied according to the local farmers spraying programme. Monitoring data indicate that physicochemical data obtained from international databases are reliable indicators of pesticide behaviour in the Western Cape of South Africa. Sensitivity analysis identified KOC as the most important parameter influencing predictions of pesticide loading derived from runoff. A comparison to monitoring data showed that the PREX successfully identified hotspot sites, gave a reasonable estimation of the relative contamination potential of different pesticides at a site and identified important routes of exposure (i.e. runoff or spray drift) of different pesticides at different sites. All pesticides detected during a monitored runoff event, were indicated as being more associated with runoff than spray drift by the PREX. The PRRI identified azinphos-methyl and chlorpyrifos as high risk pesticides towards the aquatic ecosystem. These results contribute to providing increased confidence in the use of risk indicator applications and, in particular, could lead to improved utilisation of limited resources for monitoring and management in resource constrained countries.

Is metal pollution a threat to the continued survival of the starfish in False Bay, South Africa?

Urbanisation and industrial development in the catchment area of False Bay in South Africa are increasing and concern was raised about the effect of environmental pollutants on intertidal fauna such as starfish. The aim of the present study was to obtain initial descriptive baseline data over several seasons during 2000–2001 of metal concentrations in water, sediment and body samples of the chosen cushion starfish Parvulastra exigua (Lamarck, 1816) that occurs widely in the intertidal zone of False Bay. Concentrations of cadmium, copper, lead, nickel and zinc were measured in samples of the cushion starfish, water and sediment at five localities along the coast of False Bay. The samples were chemically analysed for metals by atomic spectrophotometry. The highest individually measured concentrations of cadmium (Cd) in starfish and sediment were found in the northern coastal region between Strand and Muizenberg where most industrial activity and human settlement occur. Large variation in concentrations of all metals occurred between localities and seasons. The mean concentrations of Cd and Pb in water and sediment were in a few instances slightly higher than the recommended levels or target values of the South African marine water and sediment quality norms but still lower than those in various developed countries. Indications are that the bay was at the time of this study still less contaminated by metals in comparison with the coastal waters of various other countries. The accumulation of nonessential metals such as cadmium and lead in both sediment and bodies of starfish was nevertheless such that it can be assumed that environmental concentrations in some parts of the bay could over time build up to levels that are detrimental to the species as well as their predators. This study provided evidence that the cushion starfish in False Bay is exposed to several metals of which some are potentially hazardous since they tend to gradually accumulate in animal bodies. Risk assessment, however, requires additional information about the causal relationship between exposure and biological effects at the cellular, organismic and population levels before informed decisions can be made whether the threat to starfish is such that intervention is required.

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.

Effects of low-dosed imidacloprid pulses on the functional role of the caged amphipod Gammarus roeseli in stream mesocosms

Effects of two series of imidacloprid pulses on caged amphipods (Gammarus roeseli) and their shredder efficiency for litter decomposition were studied for 70 days as part of a comprehensive stream mesocosm experiment. The duration of each imidacloprid pulse of 12µgL(-1) was 12h. About 250mL cages with an initial stock of 10 adult gammarids together with different conditioned litter substrates were used. Beside alder leaves (Alnus glutinosa), straw (× Triticosecale) was also used in different trials and tested for its suitability to serve as litter substrate. Results from tracer and microprobe measurements approved the suitability of the test system under low-flow condition of 10cms(-1) in the surrounding stream water. Population development followed a logistic growth function with a carrying capacity of 200 Ind cage(-1) for alder and 161 for straw. In the course of the study, the F1 generation reached sexual maturity and F2 offspring appeared. Increased nitrogen contents of gammarid-free trials compared to stocked ones after 70 days indicated that biofilm on both substrates was an important food source for G. roeseli. However, increased shredding activity by gammarids was only detected for alder during the second pulse series. During the remaining time and also for straw, losses of coarse particular organic matter were quite constant and slow indicating the dominance of transport limited decomposition processes on the litter surfaces. No effect of imidacloprid pulses on population levels and litter decomposition could be detected. However, the number of brood carrying females was reduced in the treatments compared to the control groups in the last 3 weeks of the study. In conclusion, repeated low-level and short-term exposition may have adverse long-term effects on G. roeseli in the field with regard to both the population size and the functional role as key shredder.

A refined aquatic ecological risk assessment for a pyrethroid insecticide used for adult mosquito management

The use of pyrethroid insecticides has increased substantially throughout the world over the past few decades as the use of organophorous, carbamate, and organochlorine insecticides is being phased out. Pyrethroids are the most common class of insecticides for ultralow-volume (ULV) aerosol applications used to manage high densities of adult mosquitoes. Pyrethroids are highly toxic to nontarget organisms such as certain aquatic organisms, and there have been concerns about the effect of applications of ULV insecticides on these organisms. To address the uncertainties associated with the risks of ULV applications and the contradictory findings of other ecological risk assessments, the authors performed a probabilistic aquatic ecological risk assessment for permethrin using actual environmental deposition on surfaces to estimate permethrin concentrations in water. The present study is the first ecological risk assessment for pyrethroids to quantitatively integrate the reduction in bioavailability resulting from the presence of dissolved organic matter. As part of the risk assessment, the authors incorporated a species sensitivity distribution to take into account the differences in toxicity for different species. The 95th percentile estimated concentration would result in less than 0.0001% of the potentially affected fraction of species reaching the lethal concentration that kills 50% of a population. The results of the present study are supported by the weight of evidence that pyrethroids applied by ground-based ULV equipment will not result in deleterious effects on aquatic organisms.

Closer to reality--the influence of toxicity test modifications on the sensitivity of Gammarus roeseli to the insecticide imidacloprid

Laboratory toxicity test designs are far from reality and therefore extrapolations to field situations may be more difficult. In laboratory experiments with the amphipod Gammarus roeseli exposed to the insecticide imidacloprid it was investigated if test conditions closer to reality influences its sensitivity and if it is possible to extrapolate results from these laboratory tests to results from a stream mesocosm study. Experiments were run by varying medium, temperature, size, and seasonal origin of gammarids. Age and seasonal aspects had strongest effects with juveniles and animals taken from a spring population being most sensitive with an EC₅₀ (96 h) of 14.2 μg L⁻¹ imidacloprid. The test designs closest to the conditions in the stream mesocosms reflected best the results in mesocosms study on basis of LOEC values. However, the EC(x) extrapolation failed to predict the effects of short term imidacloprid pulses in the field.

Toxicity assessment of 45 pesticides to the epigeic earthworm Eisenia fetida

This study was conducted to investigate comparative toxicity of 45 pesticides, including insecticides, acaricides, fungicides, and herbicides, toward the epigeic earthworm Eisenia fetida. Results from a 48-h filter paper contact test indicated that clothianidin, fenpyroximate, and pyridaben were supertoxic to E. fetida with LC(50) values ranging from 0.28 (0.24-0.35) to 0.72 (0.60-0.94) μg cm(-2), followed by carbaryl, pyridaphenthion, azoxystrobin, cyproconazole, and picoxystrobin with LC(50) values ranging from 2.72 (2.22-0.3.19) to 8.48 (7.38-10.21) μg cm(-2), while the other pesticides ranged from being relatively nontoxic to very toxic to the worms. When tested in artificial soil for 14 d, clothianidin and picoxystrobin showed the highest intrinsic toxicity against E. fetida, and their LC(50) values were 6.06 (5.60-6.77) and 7.22 (5.29-8.68) mg kg(-1), respectively, followed by fenpyroximate with an LC(50) of 75.52 (68.21-86.57) mgkg(-1). However, the herbicides fluoroglycofen, paraquat, and pyraflufen-ethyl exhibited the lowest toxicities with LC(50) values>1000 mg kg(-1). In contrast, the other pesticides exhibited relatively low toxicities with LC(50) values ranging from 133.5 (124.5-150.5) to 895.2 (754.2-1198.0) mg kg(-1). The data presented in this paper provided useful information for evaluating the potential risk of these chemicals to soil invertebrates.

A review of rapid transport of pesticides from sloping farmland to surface waters: processes and mitigation strategies

Pesticides applied to sloping farmland may lead to surface water contamination through rapid transport processes as influenced by the complex topography and high spatial variability of soil properties and land use in hilly or mountainous regions. However, the fate of pesticides applied to sloping farmland has not been sufficiently elucidated. This article reviews the current understanding of pesticide transport from sloping farmland to surface water. It examines overland flow and subsurface lateral flow in areas where surface soil is underlain by impervious subsoil or rocks and tile drains. It stresses the importance of quantifying and modeling the contributions of various pathways to rapid pesticide loss at catchment and regional scales. Such models could be used in scenario studies for evaluating the effectiveness of possible mitigation strategies such as constructing vegetated strips, depressions, wetlands and drainage ditches, and implementing good agricultural practices. Field monitoring studies should also be conducted to calibrate and validate the transport models as well as biophysical-economic models, to optimize mitigation measures in areas dominated by sloping farmland.

Trends in Pesticide Concentrations in Streams of the Western United States, 1993-2005

Trends in pesticide concentrations for 15 streams in California, Oregon, Washington, and Idaho were determined for the organophosphate insecticides chlorpyrifos and diazinon and the herbicides atrazine, s-ethyl diproplythiocarbamate (EPTC), metolachlor, simazine, and trifluralin. A parametric regression model was used to account for flow, seasonality, and antecedent hydrologic conditions and thereby estimate trends in pesticide concentrations in streams arising from changes in use amount and application method in their associated catchments. Decreasing trends most often were observed for diazinon, and reflect the shift to alternative pesticides by farmers, commercial applicators, and homeowners because of use restrictions and product cancelation. Consistent trends were observed for several herbicides, including upward trends in simazine at urban-influenced sites from 2000 to 2005, and downward trends in atrazine and EPTC at agricultural sites from the mid-1990s to 2005. The model provided additional information about pesticide occurrence and transport in the modeled streams. Two examples are presented and briefly discussed: (1) timing of peak concentrations for individual compounds varied greatly across this geographic gradient because of different application periods and the effects of local rain patterns, irrigation, and soil drainage and (2) reconstructions of continuous diazinon concentrations at sites in California are used to evaluate compliance with total maximum daily load targets.

Ability of four emergent macrophytes to remediate permethrin in mesocosm experiments

Increased focus is being placed on the ability of native vegetation to mitigate potential harmful effects of agricultural runoff, especially pyrethroid insecticides. Replicate 379 L Rubbermaid tubs (1.25 m [l] x 0.6 m [w] x 0.8 m [h]) were planted with individual species of cutgrass (Leersia oryzoides), cattails (Typha latifolia), bur-reed (Sparganium americanum), and powdery alligator-flag (Thalia dealbata), all common wetland macrophytes found in the Mississippi Delta, USA, agricultural region. Permethrin-enriched water (target concentration, 5 microg L(-1)) was pumped in at a 4-h hydraulic retention time at one end of the tub and discharged at the far end. Water samples were collected from discharge at 1-h intervals for 12 h and analyzed for permethrin concentrations. Permethrin removal rates were compared for the four different plant treatments and nonvegetated sediment-water controls. Results indicated that no particular single plant species was more effective at removing permethrin in water relative to unplanted controls. Overall mass reductions (from inflow to outflow) for cis-permethrin ranged from 67% +/- 6% in T. latifolia to 71% +/- 2% in L. oryzoides. The trans-permethrin overall mass reductions ranged from 76% +/- 4% in S. americanum to 82% +/- 2% in the unplanted control. Sediment and plant samples collected at the study conclusion indicated that 77%-95% of measured permethrin mass was associated with sediment for mesocosms planted with L. oryzoides, T. latifolia, and T. dealbata. Conversely, mesocosms planted with S. americanum had 83% of measured mass associated with the plant material. Specific plant-pesticide retention studies can lead to improved planning for best management practices and remediation techniques such as constructed wetlands and vegetated agricultural drainage ditches.

Sorption and photodegradation of chlorpyrifos on riparian and aquatic macrophytes

Surface water bodies may become contaminated via spray drift following pesticide application. In this investigation, the photodegradation and sorption of chlorpyrifos was studied in four riparian macrophytes representative of Mediterranean flora (Phragmites australis, Iris pseudacorus, Equisetum pratense and Typha latifolia). The results of experiments with both the active ingredient and the formulation DURSBAN 48 EC confirm the ability of these species to interact with chemicals such as chlorpyrifos. The maximum sorption of chlorpyrifos at equilibrium was observed in Phragmites australis (22%). And, the maximum instantaneous sorption of chlorpyrifos was observed in the dried biomass of Phragmites australis (49%). The epicuticular waxes present on leaves influence photodegradation processes, resulting in a decrease in chlorpyrifos persistence depending on the nature of the extract. The half-life of chlorpyrifos residues in leaf waxes decreased from 34 to 99 minutes when irradiated.

Aquatic risk assessment of pesticides in surface waters in and adjacent to the Everglades and Biscayne National Parks: I. Hazard assessment and problem formulation

An aquatic risk assessment under the U.S. Environment Protection Agency (EPA) ecological risk framework was conducted for atrazine, metolachlor, malathion, chlorpyrifos, and endosulfan in the C-111 freshwater basin (eastern boundary of the Everglades National Park), northeast Florida Bay, and south Biscayne Bay in South Florida. Based on the use of the hazard quotient approach, measured concentrations of chlorpyrifos and endosulfan in surface waters suggest potential hazards to aquatic organisms and were, therefore, considered as chemicals of potential ecological concern (COPECs). The problem formulation included an overview of the physical/chemical and environmental fate characteristics and aquatic toxicology of the COPECs. Background surface water exposure concentrations of endosulfan and toxicity data from laboratory and field studies indicate that fish and invertebrate mortality may be a concern when endosulfan is applied in agricultural areas near aquatic ecosystems.

The impact of agricultural runoff on the quality of two streams in vegetable farm areas in Ghana

A study of two small streams at Akumadan and Tono, Ghana, was undertaken during the rain and dry season periods between February 2005 and January 2006 to investigate the impact of vegetable field runoff on their quality. In each stream we compared the concentration of current-use pesticides in one site immediately upstream of a vegetable field with a second site immediately downstream. Only trace concentrations of endosulfan and chlorpyrifos were detected at both sites in both streams in the dry season. In the wet season, rain-induced runoff transported pesticides into downstream stretches of the streams. Average peak levels in the streams themselves were 0.07 microg L(-1) endosulfan, 0.02 microg L(-1) chlorpyrifos (the Akumadan stream); 0.04 microg L(-1) endosulfan, 0.02 microg L(-1) chlorpyrifos (the Tono stream). Respective average pesticide levels associated with streambed sediment were 1.34 and 0.32 microg kg(-1) (the Akumadan stream), and 0.92 and 0.84 microg kg(-1) (the Tono stream). Further investigations are needed to establish the potential endosulfan and chlorpyrifos effects on aquatic invertebrate and fish in these streams. Meanwhile measures should be undertaken to reduce the input of these chemicals via runoff.

The use of Chironomus riparius larvae to assess effects of pesticides from rice fields in adjacent freshwater ecosystems

A bioassay with Chironomus riparius larvae, using larval development and growth as endpoints, was carried out inside a rice field and in the adjacent wetland channel in Portugal, during pesticide treatments (molinate, endosulfan and propanil) to determine impact caused by pesticide contamination in freshwater ecosystems. The bioassay was also performed under laboratory conditions, to assess whether in situ and laboratory bioassays demonstrated comparable results. Growth was inhibited by concentrations of endosulfan (2.3 and 1.9 microgL(-1) averages) in water from rice field in both the field and laboratory, and by concentrations of endosulfan (0.55 and 0.76 microgL(-1) averages) in water from the wetland channel in the laboratory bioassay, while development was not affected. C. riparius larvae were not affected by molinate and propanil concentrations. The results indicate that endosulfan treatments in rice fields may cause an ecological impairment in adjacent freshwater ecosystems. The results also indicate that laboratory testing can be used to assess in situ toxicity caused by pesticide contamination.

Inhibition of rainbow trout acetylcholinesterase by aqueous and suspended particle-associated organophosphorous insecticides

Spraydrift and edge-of-field runoff are important routes of pesticide entry into streams. Pesticide contamination originating from spraydrift usually resides in the water phase, while pesticides in contaminated runoff are to a large extent associated with suspended particles (SPs). The effects of two organophosphorous insecticides (OPs), chloropyrifos (CPF) and azinphos-methyl (AZP), on acetylcholinesterase (AChE) activity in rainbow trout were compared between two exposure scenarios, simulating spraydrift- and runoff-borne contamination events in the Lourens River (LR), Western Cape, South Africa. NOECs of brain AChE inhibition, determined after 1h of exposure followed by 24h of recovery, were 0.33microgl(-1) for aqueous CPF, 200mgkg(-1) for SP-associated CPF and 20mgkg(-1) for SP-associated AZP (at 0.5gl(-1) SP). The highest aqueous AZP concentration tested (3.3microgl(-1)) was without significant effects. Previously reported peak levels of aqueous CPF in the LR ( approximately 0.2microgl(-1)) are close to its NOEC (this study), suggesting a significant toxicological risk to fish in the LR. By contrast, reported levels of SP-associated OPs in the LR are 20-200-fold lower than their NOECs (this study). In a comparative in situ study, trout were exposed for seven days at agricultural (LR2, LR3) and upstream reference (LR1) sites. No runoff occurred during the study. Brain AChE was significantly inhibited at LR3. However, OP levels at LR3 (CPF 0.01microgl(-1); AZP 0.14microgl(-1)) were minor compared to concentrations having effects in the laboratory (see above). Additionally, muscle AChE activity was significantly higher in caged trout from LR1 than in animals maintained in laboratory tanks.

The impact of organophosphate pesticides in orchards on earthworms in the Western Cape, South Africa

Earthworm population density was measured in and adjacent to an orchard in an agricultural area in the Western Cape, South Africa. Worm densities were very low in orchards (22/m(2)) compared to adjacent uncultivated fields (152/m(2)) at a distance from the orchards. The possible effect of organophosphate pesticides on the earthworms was investigated. Background soil concentrations of chlorpyrifos prior to the start of the spraying season were low (0.2-2.7 microg/kg) but persistent for up to 6 months after the last spraying event, and the pesticide was, as a result of rainfall, transported to nontarget areas by runoff. Background concentrations of azinphos methyl were higher than those of chlorpyrifos (1.6-9.8 microg/kg) but not detectable 2 weeks after a spraying event. Azinphos methyl was mostly transported by wind (spray drift) to adjacent areas. A microcosm study indicated effects of chlorpyrifos on earthworms as determined by measuring biomass change and Cholinesterase inhibition. It is concluded that earthworms were affected detrimentally by the pesticides due to chronic (chlorpyrifos) and intermittent (azinphos methyl) exposure.

Biomarker response and biomass change of earthworms exposed to chlorpyrifos in microcosms

Background levels of chlorpyrifos and earthworm abundance were determined in an orchard and adjacent areas on a farm in the Western Cape, South Africa before these areas were again sprayed with this organophosphate. The background concentrations ranged from 0.2 microg/kg dm in the spray drift area adjacent to the orchard to 10.18 microg/kg dm on the slope in the run off area. In the target area the chlorpyrifos concentrations varied from a mean of 15.25 +/- 10.0 microg/kg directly after spraying to a mean of 7.0 +/- 0.9 microg/kg 6 months later and in the nontarget area they varied from a mean of 55.0 +/- 35 microg/kg to 12.0 +/- 5 microg/kg after 6 months. Chlorpyrifos was therefore still present in the field soils, but at lower concentrations, up to 6 months after the last spraying event. Earthworm abundance and population densities were very low. Only Aporrectodea caliginosa was found and the densities were much lower in the orchards (22 per m(2)) than in the nontarget areas (98.3 per m(2)). Microcosm studies were undertaken to relate biomarker responses to chlorpyrifos with biomass changes. Microcosms were filled with soil from the same areas and earthworms of the species A. caliginosa were introduced. The microcosms were treated with a series of concentrations of chlorpyrifos in the laboratory under controlled conditions. These concentrations were chosen to fall within the background ranges found in the soils. The biomass of the worms was determined regularly for a period of 5 weeks and worms in a state of estivation were noted. Earthworms were removed from the microcosms for biomarker tests: for cholinesterase (ChE) inhibition assays every week and for a neutral red retention determination 2 weeks after the exposures started. The most prominent biomass loss was noted in earthworms exposed to the highest pesticide concentration of 8.0 microg/kg. Estivation was higher among earthworms exposed to higher exposure concentrations. Inhibition of ChE increased with higher exposure concentrations and with time but there was no clear dose-related response. A clear dose-related response with exposure concentration was established for the neutral red retention assay. A correlation between ChE inhibition and biomass change existed directly after the second application of chlorpyrifos.

Mitigation of azinphos-methyl in a vegetated stream: comparison of runoff- and spray-drift

The effectiveness of aquatic macrophytes in reducing runoff- and spray-drift-induced azinphos-methyl (AZP) input was compared in a vegetated stream. Water, sediment and plant samples were taken at increasing distances from a point of input during a spray-drift event and two runoff (10 and 22 mm/day) events. Peak concentrations of AZP decreased significantly (R2=0.99; p<0.0001; n=5) from 0.24 microg/l to 0.11 microg/l during the 10mm runoff event. No reduction took place during the 22 mm event. AZP concentrations were reduced by 90% following spray-drift input, with peak concentrations decreasing significantly (R2=0.93; p=0.0084; n=5) from 4.3 microg/l to 1.7 microg/l with increasing distance from the point of input. Plant samples taken after the spray-drift event showed increased AZP concentrations in comparison to before the event indicating sorption of the pesticide to the macrophytes. Although peak concentrations of AZP were as effectively mitigated during the 10mm runoff event as during the spray-drift event, predictive modelling revealed that maximum concentrations expected during a worst-case scenario 10mm runoff event (0 days after application) are an order of magnitude lower than what can be expected for a worst-case spray-drift and 22 mm runoff event, suggesting that spray-drift-derived pesticide concentrations are more effectively mitigated than those of runoff.

Transport of commercial endosulfan through a column of aggregated vineyard soil by a water flux simulating field conditions

Endosulfan is a potentially harmful, degradation resistant pesticide that is found in soils where it has been used. Despite being hydrophobic and having high affinity for soil matrix components, it has also been found in groundwater. To investigate this behavior, we studied the passage of a commercial emulsified formulation through a column of aggregated vineyard soil under simulated light rain. Breakthrough data were obtained using gas chromatography with electron capture detection to determine the concentration of endosulfan in samples extracted from the column periodically at several depths. These data, and analogous data obtained previously for the passage of bromide, were analyzed using the program CXTFIT v.2. Analysis of the bromide data strongly suggested the existence of preferential flow paths in the column. The endosulfan data were adequately accounted for by a model in which the preferential flow and nonpreferential flow regions are almost isolated from each other. These regions differ also as regards both the partition of endosulfan between soil and soil solution and the rate at which reversibly adsorbed endosulfan is transformed into irreversibly adsorbed endosulfan. The "irreversibility" sink term accounts also for biological and chemical degradation of endosulfan. The findings imply that soil humidity favors the transport of commercial endosulfan by the formation and maintenance of preferential flow paths in soil, controlling both the presence of endosulfan in groundwater and its high persistence in soil.

Deposition and dissipation of chlorpyrifos in surface water following vineyard applications in northern Italy

Chlorpyrifos is an insecticide approved globally for use on a wide range of crops. Laboratory studies indicate that chlorpyrifos is toxic to fish and aquatic invertebrates, and so the adoption of practices that reduce aquatic exposure following use should be encouraged. This study assessed the exposure of surface water to the spray-drift of chlorpyrifos and the subsequent contamination of a realistic worst-case edge-of-field ditch in a vineyard in Northern Italy. Chlorpyrifos (DURSBAN 480 EC [Dow Elanco, Indianapolis, IN, USA]) was applied according to local Good Agricultural Practice (GAP) on two vineyard plots using atomizer equipment. Drift deposition and subsequent dissipation of chlorpyrifos were then monitored in an adjacent, common ditch, with an inherent buffer zone of approximately 7 m between the treated area and the ditch. The results showed that the drift loadings under the study conditions could reach predicted levels from standard spray-drift tables. However, the measured drift was highly variable due to physical factors such as the crop canopy and the distribution of vines within the rows. The amount of chlorpyrifos deposited onto the surface of the ditch water and intercepted by paper strips was approximately 2% of the applied amount after the two applications, with a maximum concentration of approximately 0.3 microg L(-1) immediately after the first application and 0.09 microg L(-1) after the second, which then dissipated from the water column within 12 to 24 h. The results showed that drift deposition spatially was variable and that chlorpyrifos residues dissipated rapidly from this surface water body. Both aspects are considered important in order to refine the aquatic risk assessment at a higher tier for both registration and management purposes.

Chlorpyrifos-methyl dissipation in a small adjacent water body following application to citrus

Chlorpyrifos-methyl use in citrus, vineyards and vegetables is extensive and it has become an essential component of pest control in Southern European regions. The objective of this study was to assess surface water and sediment exposure to chlorpyrifos-methyl (RELDAN 22) under field conditions in a citrus orchard in Sicily (Italy). Pesticide drift loadings were measured in a small surface water body situated 0.5-1.0 m from the edge of the treated field. Measured drift values after the application were between 0.04% and 0.19% of the theoretical applied dose and were highly variable. However, the loadings were lower than those measured by other authors, also lower than predicted by regulatory drift models (95th percentile) typically used for aquatic risk assessment in Europe. Most of the variability occurred due to fluctuating wind speed and direction. In water samples collected in the surface water adjacent to the target field, chlorpyrifos-methyl was detected immediately after application, with concentrations ranging from less than the limit of quantification of the analytical method (0.05 microg/l) to a maximum of 0.08 microg/l. Predicted environmental concentrations in water, using the TOXSWA model, were similar to the measured data when measured drift data from the field experiment were used as inputs.

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.

Fate and effects of azinphos-methyl in a flow through wetland in South Africa

Our knowledge about the effectiveness of constructed wetlands in retaining agricultural nonpoint-source pesticide pollution is limited. A 0.44-ha vegetated wetland built along a tributary of the Lourens River, Western Cape, South Africa, was studied to ascertain the retention, fate, and effects of spray drift-borne azinphos-methyl (AZP). Composite water samples taken at the inlet and outlet during five spray drift trials in summer 2000 and 2001 revealed an overall reduction of AZP levels by 90 +/- 1% and a retention of AZP mass by 61 +/- 5%. Samples were collected at the inlet outlet, and four platforms within the wetland to determine the fate and effect of AZP in the wetland after direct spray drift deposition in the tributary 200 m upstream of the inlet. Peak concentrations of AZP decreased, and the duration of exposure increased from inlet (0.73 microg/L; 9 h) via platforms 1 and 4 to outlet (0.08 microg/L; 16 h). AZP sorbed to plants or plant surfaces, leading to a peak concentration of 6.8 microg/kg dw. The living plant biomass accounted for 10.5% of the AZP mass initially retained in the wetland, indicating processes such as volatilization, photolysis, hydrolysis, or metabolic degradation as being very important AZP was not detected in sediments. Water samples taken along two 10-m transects situated perpendicular to the shore indicated a homogeneous horizontal distribution of the pesticide: 0.23 +/- 0.02 and 0.14 +/- 0.04 microg/L (n = 5), respectively. Both Copepoda (p = 0.019) and Cladocere (p = 0.027) decreased significantly 6 h postdeposition and remained at reduced densities for at least 7 d. In parallel, the chlorophyll a concentration showed an increase, although not significant, within 6 h of spray deposition. The study highlights the potential of constructed wetlands as a risk-mitigation strategy for spray drift-related pesticide pollution.

Comparison of spray drift- and runoff-related input of azinphos-methyl and endosulfan from fruit orchards into the Lourens River, South Africa

Spray drift and edge-of-field runoff are regarded as important routes of nonpoint-source pesticide input into aquatic surface waters, with current regulatory risk assessment in Europe focussing largely on spray drift. However, the two routes of entry had rarely been compared directly in the same catchment. To this end, the concentrations and loads of the current-use insecticides azinphos-methyl (AZP) and endosulfan (END) were monitored in the Lourens River, South Africa downstream of a 400-ha fruit orchard area during normal farming practice. Spray drift-related peak pesticide levels in the tributaries were in the range of 95th-percentiles of standard drift values according to regulatory risk assessment procedures. Resulting concentrations in Lourens River water samples (n = 3) at a discharge of 0.28 m3/s were as high as 0.04 +/- 0.01 microg/l AZP and 0.07 +/- 0.02 microg/l END. Pesticide levels at the same site during runoff following 3 storm events varying in rainfall between 6.8 and 18.4 mm/d (discharge: 7.5-22.4 m3/s) were considerably higher: by factors between 6 and 37 for AZP (0.26-1.5 microg/l) and between 2 and 41 for END (0.13-2.9 microg/l). Levels of pesticides associated with suspended particles were increased during runoff only up to 1247 microg/kg AZP and 12082 microg/kg END. A possible reason for the relative importance of runoff is that runoff largely integrates potential pesticide input over both time and space, because the prerequisites for the occurrence of runoff in terms of application and plot characteristics as well as meteorological conditions are far less specific than for spray drift. A probability analysis based on pesticide application patterns and 10-yr rainfall data indicates that the frequencies of rainfall events > or = 10 and > or = 15 mm/d are 3.4 and 1.7 per spraying season, respectively.