Attenuation of insecticide impact by a small wetland in a stream draining a horticultural basin in Argentina.

Horticulture has greatly increased in Argentina in recent decades mainly due to increasing greenhouse utilization and agrochemical consumption, thus representing a threat to adjacent water bodies. Riparian wetlands, however, could attenuate agrochemical contamination. The present work therefore compared insecticide concentrations in bottom sediments in addition to sediment toxicity to the amphipod Hyalella curvispina and investigated the macroinvertebrate composition upstream and downstream from a natural wetland in a small stream draining a basin undergoing intense horticultural production. The wetland surface was covered by macrophytes, mainly Thypha sp., and the insecticide concentrations measured downstream from the wetland were significantly lower, at roughly 19% of the upstream values. The growth rates of H. curvispina were significantly higher when exposed to the sediments downstream from the wetland, while the macroinvertebrate-assemblage composition was significantly different upstream and downstream: the snail Pomacea canaliculata was the dominant species upstream while the amphipod H. curvispina was dominant downstream. Pomacea canaliculata is often the dominant species in the regional streams draining agriculture and horticultural basins. Hyalella curvispina is sensitive to pesticide toxicity and is often dominant in streams draining extensive livestock basins and within a biosphere reserve. We conclude that riparian wetlands effectively attenuate horticulture contamination in pampean streams and should therefore be preserved and restored.

Insecticide toxicity to Hyalella curvispina in runoff and stream water within a soybean farm (Buenos Aires, Argentina).

Toxicity to the locally dominant amphipod Hyalella curvispina was assessed in a first-order stream running through a cultivated farm. Cypermethrin, chlorpyrifos, endosulfan and glyphosate were sprayed throughout the studied period. Toxicity was assayed under controlled laboratory conditions with runoff and stream water samples taken from the field under steady state and flood conditions. Ephemeral toxicity pulses were observed as a consequence of farm pesticide applications. After pesticide application, runoff water showed 100% mortality to H. curvispina for 1 month, but no mortality thereafter. Toxicity persistence was shortest in stream water, intermediate in stream sediments and longest in soil samples. Runoff had a more important toxicity effect than the exposure to direct aerial fumigation. The regional environmental features determining fast toxicity dissipation are discussed.

Effect of aquatic vegetation on the persistence of cypermethrin toxicity in water.

Soybean production in Argentina comprises 15 million ha. Cypermethrin is the main insecticide applied amounting 150 g of active ingredient per hectare, thus representing roughly 2.3 thousand tons yearly released to the environment. Toxicity pulses have been observed in small streams draining agricultural basins, most of them sustaining macrophyte growth. Cypermethrin concentrations and its toxicity to the amphipod Hyalella curvispina was compared following an addition to laboratory mesocosms with and without a vegetation cover of the floating macrophyte Lemna sp. Both concentrations and toxicity decreased faster in the treatments covered with Lemna. Fast adsorption of the hydrophobic pesticide to the roots and fronds of Lemna was suggested.

Toxicity persistence following an experimental cypermethrin and chlorpyrifos application in Pampasic surface waters (Buenos Aires, Argentina).

The Pampa plain is intensively cultivated, the genetically modified glyphosate-resistant soybean being the main culture. A small first-order stream draining a cultured farm was studied. During the dry 2007 spring, the channel became a wetland with remnant intercalated shallow pools. Toxicity persistence of cypermethrin and chlorpyrifos to the amphipod Hyallela curvispina was assessed following a simulated plane application in the recently formed pools. In situ exposures and laboratory toxicity tests were performed. An ephemeral toxicity pulse lasting 4 h after the application and mortality cessation following that was observed.

Effects of the herbicide Roundup on freshwater microbial communities: a mesocosm study.

The impact of the widely used herbicide glyphosate has been mainly studied in terrestrial weed control, laboratory bioassays, and field studies focusing on invertebrates, amphibians, and fishes. Despite the importance of phytoplankton and periphyton communities at the base of the aquatic food webs, fewer studies have investigated the effects of glyphosate on freshwater microbial assemblages. We assessed the effect of the commercial formulation Roundup using artificial earthen mesocosms. The herbicide was added at three doses: a control (without Roundup) and two treatments of 6 and 12 mg/L of the active ingredient (glyphosate). Estimates of the dissipation rate (k) were similar in the two treatments (half-lives of 5.77 and 7.37 d, respectively). The only two physicochemical parameters showing statistically significant differences between treatments and controls were the downward vertical spectral attenuation coefficient kd(lambda), where lambda is wavelength, and total phosphorus concentration (TP). At the end of the experiment, the treated mesocosms showed a significant increase in the ratio kd(490 nm)/k(d)(550 nm) and an eightfold increase in TP. Roundup affected the structure of phytoplankton and periphyton assemblages. Total micro- and nano-phytoplankton decreased in abundance in treated mesocosms. In contrast, the abundance of picocyanobacteria increased by a factor of about 40. Primary production also increased in treated mesocosms (roughly by a factor of two). Similar patterns were observed in the periphytic assemblages, which showed an increased proportion of dead: live individuals and increased abundances of cyanobacteria (about 4.5-fold). Interestingly, the observed changes in the microbial assemblages were captured by the analysis of the pigment composition of the phytoplankton, the phytoplankton absorption spectra, and the analysis of the optical properties of the water. The observed changes in the structure of the microbial assemblages are more consistent with a direct toxicological effect of glyphosate rather than an indirect effect mediated by phosphorus enrichment.

Assessment of insecticide contamination in runoff and stream water of small agricultural streams in the main soybean area of Argentina.

The first- and second-order streams, Brown and Horqueta, respectively, which are located in the main area of soybean production in Argentina were examined for insecticide contamination caused by runoff from nearby soybean fields. The insecticides most widely used in Argentina (chlorpyrifos, cypermethrin and endosulfan) were detected in sediments, suspended particles and water. Highest concentrations in suspended particles were 318 microg/kg for endosulfan in the stream Horqueta, while 226 microg/kg chlorpyrifos and 13.2 microg/kg cypermethrin were measured in the stream Brown. In the Horqueta stream 150 and 53 microg/kg chlorpyrifos and cypermethrin were detected in runoff sediments, respectively. Whereas cypermethrin concentrations in the suspended particles were relatively low, levels in the floodwater of Brown reached 0.7 microg/l. The highest chlorpyrifos concentration in floodwater was 0.45 microg/l in Brown. However, endosulfan was not detected in the water phase. In runoff water the highest concentrations measured were 0.3 microg/l for chlorpyrifos in Horqueta and 0.49 microg/l for cypermethrin in the Brown stream. On five sampling dates during the pesticide application period in Brown stream (2002/2003) the concentration of chlorpyrifos and cypermethrin in runoff and/or floodwater exceeded the water quality criteria for freshwater mentioned in this study. In three cases this insecticide concentration was measured in stream water, indicating an acute risk to aquatic life. The acute toxicity-exposure-ratio (TER) for chlorpyrifos and cypermethrin also shows an acute risk for aquatic invertebrates in the Brown stream. In the Horqueta chlorpyrifos concentrations in the runoff exceeded the safety levels three times during the application period (2001/2002), potentially endangering the aquatic fauna. Effects on aquatic macroinvertebrates after insecticide contamination were reported in earlier studies in Horqueta stream.

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 endosulfan contamination and aquatic macroinvertebrate response in rural basins near Buenos Aires, Argentina.

Information in the open literature about the fate and effects of pesticides in small streams from agricultural areas of Argentina is very rare. The objective of the present work was to study the pesticide contamination and potential biological effects in basins that have undergone intense agricultural activity, mainly related to the cultivation of soybeans. Three streams (Maguire, Helves, and Horqueta) with a low-flow discharge (0.1 and 0.2 m3/s) in March close to the city of Arrecifes were studied during the period of maximum insecticide application, between February and April 2001. Various sampling devices were installed to trap suspended particles, runoff, and floodwater plus sediment throughout the study period. The suspended-particle samples were analyzed for the insecticides endosulfan (END), chlorpyrifos, and cypermethrin. Water chemistry and the macroinvertebrate communities were assessed on four occasions and the organismic drift was measured continuously. Following a 184-mm rainfall on March 1, 2001, beta-endosulfan concentrations up to 318 and 43 microg/kg were measured from suspended-particle samples from Horqueta and Helves, respectively. No END contamination was detected in Maguire. Chlorpyrifos and cypermethrin were not detected in any of the streams. A significant decrease in the average macroinvertebrate species density was observed in Horqueta (from 12.8 +/- 0.5 to 9 +/- 0.7 species; ANOVA, p < 0.05) and Helves (from 10.8 +/- 1.7 to 3.3 +/- 1.3 species; p < 0.001) following the same rainfall event at the beginning of March, while the species density in Maguire remained constant at 7.9 +/- 0.3 species. The runoff primarily reduced species abundances of Odonata and Ephemeroptera significantly (p < 0.01) in Horqueta and Helves but not in Maguire. A greater drift of Smicridae (Trichoptera) and Ephemeroptera occurred in Helves and Horqueta during this runoff event, while no changes in the macroinvertebrate drift were detectable in Maguire. This study highlights the potential pesticide effects on macroinvertebrate communities in Argentinian rural streams. It is suggested that a small wetland area formed by Maguire between the agriculturally used catchment and the sampling site contributes to the absence of contamination and effects at this site.