Freshwater Community Responses to Mixtures of Agricultural Pesticides: Synergistic Effects of Atrazine and Bifenthrin

This study was an investigation of the effects of the herbicide atrazine and the insecticide bifenthrin on lake communities. The study was conducted in two phases: in phase one, we examined the effects of environmentally realistic levels of atrazine and bifenthrin, based on published data of concentrations measured in fresh waters; in phase two, the impacts of higher levels of atrazine and bifenthrin were investigated, based on concentrations used in previous studies. The factorial designed experiment included three levels of bifenthrin (0, 1/39, and 1/287 ngL in phase one and 0, 1/125, and 1/3150 ngL in phase two) cross-classified with three levels of atrazine (0, 1/15, and 1/153 ugL in phase one and 0, 1/385, and 1/2167 ugL in phase two), with duplicate replication of each treatment combination. Pesticides were added to 5,500 L fiberglass tanks containing natural plankton assemblages and bluegill. Tanks were sampled 7 and 14 d following the first pesticide treatment and 7 d after the second pesticide addition. In phase one of the study, atrazine significantly reduced chlorophyll concentrations and turbidity on day 7 Wand had no significant impact on primary productivity or algal cell densities. Atrazine also had a significant negative effect on copepod nauplii and rotifers (days 7 and 14) and on Bosmina and particulate phosphorus in the 20-200 um size fraction (day 14). Bifenthrin significantly reduced Bosmina (days 7 and 14), cyclopoid copepodids (days 7 and 14), and copepod nauplii (day 14), however bifenthrin increased rotifers at day 7. Bifenthrin addition also increased colonial green algae and decreased particulate phosphorus in the 20-200 um size fraction on day 7 and decreased turbidity and particulate phosphorus in the >200 um size fraction on days 7 and 14. Only one fish mortality (in the high bifenthrin, no atrazine treatment combination) occurred during phase one of the study. Significant interaction effects were found only for Bosmina (day 14), rotifers (day 7), and turbidity (days 7 and 14), indicating that at the concentrations used in phase one of this study, these agricultural pesticides did not act synergistically. In phase two, higher levels of atrazine resulted in significant reductions in primary productivity, chlorophyll, green colonies, Bosmina, rotifers, and particulate phosphorus (>200 um and 20-200 um) on day 7. Bifenthrin had a negative impact on Bosmina, copepod nauplii, rotifers, primary productivity, chlorophyll, green colonies, and all particulate phosphorus fractions. In addition, 33% bluegill mortality was observed in treatment combinations with an average maximum concentration of 1/3150 ngL bifenthrin. The interaction effects found indicated that when either compound was introduced at ecologically realistic levels, its effects were essentially masked if the other toxicant was present at high concentrations

Effects of bromide and iodide on stalk secretion in the biofouling diatom Achnanthes longipes (Bacillariophyceae)

Extracellular polymeric substance (EPS) secretion was examined in the stalked marine diatom Achnanthes longipes Ag. in defined medium. This common biofouling diatom exhibited an absolute requirement for bromide for stalk production and substratum attachment, whereas elevated iodide concentrations in the growth medium inhibited stalk formation and adhesion. Varying EPS morphologtes resulted from altering bromide and iodide levels: pads, stalk‐pads, stalks, and no EPS. Cells showed no differences in growth with bromide or iodide concentrations, indicating that they were not physiologically stressed under conditions that impaired EPS secretion. Cells grown in elevated iodide secreted significantly more soluble extracellular carbohydrate into the medium, suggesting that the EPS was soluble and unable to be polymerized into a morphologically distinct gel. By replacing sulfate with methionine, the diatom lost its ability to form stalks even in the presence of bromide, indicating that free sulphate may be required for proper cross‐linking of stalk polymers. Lotus‐FITC, a fluorescent‐tagged lectin, preferentially labeled the EPS and, thus, was used to visualize and quantify EPS secretion along a bromide gradient in conjunction with an image analysis system. This technique demonstrated a direct correlation between the amount of bromide present in the medium and the specific EPS morphology formed. Copyright © 1995, Wiley Blackwell. All rights reserve

Acute -N-Methylamino-L-alanine Toxicity in a Mouse Model

The cyanobacterial neurotoxin -N-methylamino-L-alanine (BMAA) is considered to be an “excitotoxin,” and its suggested mechanism of action is killing neurons. Long-termexposure to L-BMAAis believed to lead to neurodegenerative diseases including Parkinson’s and Alzheimer’s diseases and amyotrophic lateral sclerosis (Lou Gehrig’s disease). Objectives of this study were to determine the presumptive median lethal dose (LD50), the Lowest-Observed-Adverse-Effect Level (LOAEL), and histopathologic lesions caused by the naturally occurring BMAA isomer, L-BMAA, in mice. Seventy NIH Swiss Outbred mice (35 male and 35 female) were used. Treatment group mice were injected intraperitoneally with 0.03, 0.3, 1, 2, and 3mg/g body weight L-BMAA, respectively, and control mice were sham-injected.The presumptive LD50 of L-BMAA was 3mg/g BWand the LOAEL was 2mg/g BW.There were no histopathologic lesions in brain, liver, heart, kidney, lung, or spleen in any of the mice during the 14-day study. L-BMAA was detected in brains and livers in all of treated mice but not in control mice.Males injected with 0.03mg/g BW, 0.3mg/g BW, and 3.0mg/g BW L-BMAA showed consistently higher concentrations (P \u3c 0.01) in brain and liver samples as compared to females in those respective groups

Co-occurrence of the Cyanotoxins BMAA, DABA and Anatoxin-a in Nebraska Reservoirs, Fish, and Aquatic Plants

Several groups of microorganisms are capable of producing toxins in aquatic environments. Cyanobacteria are prevalent blue green algae in freshwater systems, and many species produce cyanotoxins which include a variety of chemical irritants, hepatotoxins and neurotoxins. Production and occurrence of potent neurotoxic cyanotoxins β-N-methylamino-L-alanine (BMAA), 2,4-diaminobutyric acid dihydrochloride (DABA), and anatoxin-a are especially critical with environmental implications to public and animal health. Biomagnification, though not well understood in aquatic systems, is potentially relevant to both human and animal health effects. Because little is known regarding their presence in fresh water, we investigated the occurrence and potential for bioaccumulation of cyanotoxins in several Nebraska reservoirs. Collection and analysis of 387 environmental and biological samples (water, fish, and aquatic plant) provided a snapshot of their occurrence. A sensitive detection method was developed using solid phase extraction (SPE) in combination with high pressure liquid chromatography-fluorescence detection (HPLC/FD) with confirmation by liquid chromatography-tandem mass spectrometry (LC/MS/MS). HPLC/FD detection limits ranged from 5 to 7 μg/L and LC/MS/MS detection limits were \u3c0.5 μg/L, while detection limits for biological samples were in the range of 0.8–3.2 ng/g depending on the matrix. Based on these methods, measurable levels of these neurotoxic compounds were detected in approximately 25% of the samples, with detections of BMAA in about 18.1%, DABA in 17.1%, and anatoxin-a in 11.9%

Acute -N-Methylamino-L-alanine Toxicity in a Mouse Model

The cyanobacterial neurotoxin -N-methylamino-L-alanine (BMAA) is considered to be an "excitotoxin," and its suggested mechanism of action is killing neurons. Long-term exposure to L-BMAA is believed to lead to neurodegenerative diseases including Parkinson's and Alzheimer's diseases and amyotrophic lateral sclerosis (Lou Gehrig's disease). Objectives of this study were to determine the presumptive median lethal dose (LD 50 ), the Lowest-Observed-Adverse-Effect Level (LOAEL), and histopathologic lesions caused by the naturally occurring BMAA isomer, L-BMAA, in mice. Seventy NIH Swiss Outbred mice (35 male and 35 female) were used. Treatment group mice were injected intraperitoneally with 0.03, 0.3, 1, 2, and 3 mg/g body weight L-BMAA, respectively, and control mice were sham-injected. The presumptive LD 50 of L-BMAA was 3 mg/g BW and the LOAEL was 2 mg/g BW. There were no histopathologic lesions in brain, liver, heart, kidney, lung, or spleen in any of the mice during the 14-day study. L-BMAA was detected in brains and livers in all of treated mice but not in control mice. Males injected with 0.03 mg/g BW, 0.3 mg/g BW, and 3.0 mg/g BW L-BMAA showed consistently higher concentrations (P < 0.01) in brain and liver samples as compared to females in those respective groups

Seed Bank Viability of Inland Saline Wetland Sites in Agro-Ecosystems

Wetland restoration typically includes modifications to soils, flora, and hydrology. Will the return of wetland hydrology to former saline wetlands create conditions suitable for wetland taxa, especially saline wetland indicator species? To answer this question we evaluated the potential restoration efficacy of historical saline wetland soils by re-exposing them to wetland hydrological conditions simulated in a greenhouse. Agricultural lands contained no saline indicator plants and limited wetland species, likely due to significant and long-term land alteration. Restored wetlands showed only a few additional wetland taxa, and seeds of saline wetland plants emerged from soils of only one restored site. Because land alteration threatens the seed bank status of current saline wetlands, potential restoration sites, and even historical saline wetlands under agricultural production in Nebraska, preservation of existing sites that currently have saline dynamics and affluent seed banks may be the only means for continued restoration