Diazinon and permethrin mitigation across a grass-wetland buffer.

Vegetated buffers of different designs are often used as edge-of-field treatment practices to remove pesticides that may be entrained in agricultural runoff. However, buffer system efficacy in pesticide runoff mitigation varies widely due to a multitude of factors including, but not limited to, pesticide chemistry, vegetation composition, and hydrology. Two experimental systems, a control (no vegetation) and a grass-wetland buffer system, were evaluated for their ability to retain diazinon and permethrin associated with a simulated storm runoff. The two systems were equally inefficient at retaining diazinon (mean 9.6 % retention for control and buffer). Grass-wetland buffers retained 83 % and 85 % of cis- and trans-permethrin masses, respectively, while the control only retained 39 % and 44 % of cis- and trans-permethrin masses, respectively. Half-distances (the distance required to decrease pesticide concentration by one-half) for both permethrin isomers were 26 %-30 % shorter in grass buffers (22-23 m) than in the control (32 m). The current study demonstrates treatment efficacy was a function of pesticide properties with the more strongly sorbing permethrin retained to a greater degree. The study also demonstrates challenges in remediating multiple pesticides with a single management practice. By using suites of management practices, especially those employing vegetation, better mitigation of pesticide impacts may be accomplished.

Nutrient mitigation capacity in Mississippi Delta, USA drainage ditches.

Eutrophication and hypoxia within aquatic systems are a serious international concern. Various management practices have been proposed to help alleviate nutrient loads transported to the Gulf of Mexico and other high-profile aquatic systems. The current study examined the nutrient mitigation capacity of a vegetated (V) and non-vegetated (NV) agricultural drainage ditch of similar size and landform in the Mississippi Delta. While no statistically significant differences in ammonium, nitrate, or dissolved inorganic phosphorus mitigation between the two ditches existed, there were significant differences in total inorganic phosphorus percent load reductions (V: 36% +/- 4; NV: 71% +/- 4). However, both agricultural drainage ditches were able to mitigate nutrients, thus reducing the load reaching downstream aquatic receiving systems. Further studies examining ecosystem dynamics within drainage ditches such as sediment and plant nutrient partitioning, as well as microbial processes involved, are needed to provide a better understanding of natural nutrient variability, seasonality and flux.

Mississippi oxbow lake sediment quality during an artificial flood.

Surface sediment quality was assessed during a 35-day artificial flood in a shallow (<1.5 m) oxbow lake along the Coldwater River, Mississippi, using Hyalella azteca 28-day bioassays. Seventeen pesticides were monitored in sediments before, during and after flooding, with increases in atrazine and metolachlor concentrations coinciding with two unexpected storm events, 51 and 56 mm, during and after flooding, respectively. Mean 28-day H. azteca survival was >85% throughout this study. However, growth was affected at three sites during flooding with limited growth recovery after flooding. Patterns in observed growth impairment were associated with changes in atrazine (R(2)=0.524) and fipronil sulfone (R(2)=0.584) concentrations.

Influence of selected water quality characteristics on the toxicity of lambda-cyhalothrin and gamma-cyhalothrin to Hyalella azteca.

This study was conducted to assess the influence of suspended solids, dissolved organic carbon, and phytoplankton (as chlorophyll a) water quality characteristics on lambda-cyhalothrin and gamma-cyhalothrin aqueous toxicity to Hyalella azteca using natural water from 12 ponds and lakes in Mississippi, USA with varying water quality characteristics. H. azteca 48-h immobilization EC50 values ranged from 1.4 to 15.7 ng/L and 0.6 to 13.4 ng/L for lambda-cyhalothrin and gamma-cyhalothrin, respectively. For both pyrethroids, EC50 values linearly increased as turbidity, suspended solids, dissolved organic carbon and chlorophyll a concentrations increased.

Toxicity assessment of diazinon in a constructed wetland using Hyalella azteca.

The goal of this study was to examine the use of a constructed wetland to mitigate the ecological impacts of simulated diazinon runoff from agricultural fields into receiving waters, via 48 h aqueous and sediment bioassays using Hyalella azteca. Aqueous animal 48 h survival varied temporally and spatially in conjunction with measured diazinon concentrations. Sediment H. azteca survival varied temporally and spatially in conjunction with measured diazinon concentrations, but less than aqueous exposures, confirming that sediment bound diazinon was less bioavailable than aqueous diazinon.

Assessment of pesticide contamination in three Mississippi Delta oxbow lakes using Hyalella azteca.

Three oxbow lakes in northwestern Mississippi, USA, an area of intensive agriculture, were assessed for biological impairment from historic and current-use pesticide contamination using the amphipod, Hyalella azteca. Surface water and sediment samples from three sites in each lake were collected from Deep Hollow, Beasley, and Thighman Lakes from September 2000 to February 2001. Samples were analyzed for 17 historic and current-use pesticides and selected metabolites. Ten-day H. azteca survival and growth (as length and dry weight) were measured to determine the degree of biological impairment. Maximum number of detectable pesticides in surface water from Deep Hollow, Beasley and Thighman Lakes was 10, 11, and 17, respectively. Maximum number of detectable pesticides in lake sediments was 17, 17, and 15, respectively. Bioassay results indicated no observable survival effects on H. azteca exposed to surface water or sediment from any lake examined and no growth impairment in animals exposed to lake sediments. However, growth was significantly impaired in surface water exposures from Deep Hollow Lake (2 sites) and Beasley Lake (1 site). Statistically significant relationships between growth impairment (length) and cyanazine, methyl parathion, lambda-cyhalothrin, chlorfenapyr, and pp'DDE surface water concentrations in Deep Hollow Lake as well as trifluralin, atrazine, and methyl parathion in Beasley Lake were observed. Although pesticide frequency and concentrations were typically greater in sediment than surface water, bioassay results indicated decreased availability of these pesticides in sediment due to the presence of clay and organic carbon. Growth impairment observed in surface water exposures was likely due to complex interaction of pesticide mixtures that were present.

Effects of a homologous series of linear alcohol ethoxylate surfactants on fathead minnow early life stages.

Effects of a homologous series of three primarily linear alcohol ethoxylate surfactants were studied in laboratory flow-through 28-day early-life-stage tests with fathead minnow (Pimephales promelas Rafinesque). Surfactants were a C(9-11), C(12-13), and C(14-15) with an average of 6, 6.5, and 7 ethylene oxide units per mole of alcohol, respectively. Average measured surfactant recoveries were 103%, 81%, and 79% of nominal concentrations for the C(9-11) EO 6, C(12-13) EO 6.5, and C(14-15) EO 7 studies, respectively. Embryo survival at 48 h was not adversely affected at any of the concentrations tested. Impaired hatching and deformed fry were observed only in the C(12-13) EO 6.5 study. The 28-day LC50 values were 4.87, 2.39, and 1.02 mg/L for the C(9-11) EO 6, C(12-13) EO 6.5, and C(14-15) EO 7 surfactants, respectively. The corresponding NOECs for survival were 1.01, 1.76, and 0.74 mg/L. Posthatch fry growth was more sensitive than survival for the C(12-13) EO 6.5 and C(14-15) EO 7 surfactants. Survival of posthatch fry decreased with increasing surfactant alkyl chain length. Twenty-eight-day laboratory data were compared to 96-h laboratory, 10-day laboratory and 30-day stream mesocosm data for fathead minnow previously determined for these surfactants. Survival endpoints from the different exposures were comparable and only varied within a factor of two. Similarity of results suggests that it is possible to effectively use 96-h, 10-day, or 28-day laboratory data to predict environmental effects concentrations of these surfactants for fish. http://link.springer-ny. com/link/service/journals/00244/bibs/37n4p536.html

Gastrointestinal helminths in the river otter (Lutra canadensis) in Tennessee.

The first records of 3 helminth parasites from otters, Lutra canadensis, collected in Tennessee are reported. Digestive tracts of 91 river otters collected from 1983 to 1993 were examined for helminth parasites. Thirty otters were infected with Baschkirovitrema incrassatum, 5 otters were infected with Acanthocephalus sp., and 1 otter was infected with 2 Strongyloides lutrae. No significant differences in prevalence, mean abundance, or mean intensity of B. incrassatum occurred between counties or months. No significant differences in the prevalence or mean intensity of B. incrassatum occurred between years, but significant yearly differences in mean abundance were recorded from 1988 through 1993 (P < 0.05). There were no statistical differences in B. incrassatum parasitization between males and females or juvenile and adult otters.