Wetland macrophyte community response to and recovery from direct application of glyphosate-based herbicides.

Community-scale impacts of glyphosate-based herbicides on wetland plant communities and the magnitude of those impacts that should be considered biologically relevant are poorly understood. We contrast three different thresholds for setting biologically meaningful critical effect sizes for complex ANOVA study designs. We use each of the of the critical effect sizes to determine optimal α levels for assessment of how different concentrations of glyphosate-based herbicides affect wetland plant communities over two years of herbicide application (alone and in combination with agricultural fertilizers) and two subsequent years without herbicide (or fertilizer) application. The application of glyphosate-based herbicides was found to result in a decrease in macrophyte species richness, an increase in macrophyte species evenness, a decrease in macrophyte cover and a reduction in community similarity. There was little evidence that nutrient additions directly or indirectly affected plant community endpoints. The glyphosate effects were evident in the first year of herbicide application in 2009, and became more pronounced in the second year of herbicide application in 2010. However, when herbicides were not applied in 2011, recovery was observed in most endpoints, with the exception being species evenness, for which partial recovery was not observed until 2012. Optimal α levels differed among the three critical effect sizes for each ANOVA term and endpoint combination, however regardless of differences in α levels, conclusions were generally consistent across all critical effect sizes.

The combined influence of two agricultural contaminants on natural communities of phytoplankton and zooplankton.

Concentrations of glyphosate observed in the environment are generally lower than those found to exert toxicity on aquatic organisms in the laboratory. Toxicity is often tested in the absence of other expected co-occurring contaminants. By examining changes in the phytoplankton and zooplankton communities of shallow, partitioned wetlands over a 5 month period, we assessed the potential for direct and indirect effects of the glyphosate-based herbicide, Roundup WeatherMax(©) applied at the maximum label rate, both in isolation and in a mixture with nutrients (from fertilizers). The co-application of herbicide and nutrients resulted in an immediate but transient decline in dietary quality of phytoplankton (8.3 % decline in edible carbon content/L) and zooplankton community similarity (27 % decline in similarity and loss of three taxa), whereas these effects were not evident in wetlands treated only with the herbicide. Thus, even at a worst-case exposure, this herbicide in isolation, did not produce the acutely toxic effects on plankton communities suggested by laboratory or mesocosm studies. Indirect effects of the herbicide-nutrient mixture were evident in mid-summer, when glyphosate residues were no longer detectable in surface water. Zooplankton abundance tripled, and zooplankton taxa richness increased by an average of four taxa in the herbicide and nutrient treated wetlands. The lack of significant toxicity of Roundup WeatherMax alone, as well as the observation of delayed interactive or indirect effects of the mixture of herbicide and nutrients attest to the value of manipulative field experiments as part of a comprehensive, tiered approach to risk assessments in ecotoxicology.

C60 fullerene soil sorption, biodegradation, and plant uptake.

Assessments of potential exposure to fullerenes and their derivatives in the environment are important, given their increasing production and use. Our study focused on fate processes that determine the movement and bioavailability of fullerenes in soil. We evaluated the sorption, biodegradation, and plant uptake of C60 fullerene using (14)C-labeled C60 solutions in water produced by either solvent exchange with tetrahydrofuran or sonication/extended mixing in water. Organic carbon appeared to have an important influence on C60 soil sorption. The log Koc values for (14)C60 were equivalent for sandy loam and silt loam (3.55 log[mL/g]) but higher for loam (4.00 log[mL/g]), suggesting that other factors, such as pH, clay content and mineralogy, and cation exchange capacity, also influence C60 soil sorption. There was little (14)CO2 production in the silt loam or the sandy loam soil after 754 and 328 days, respectively, suggesting high resistance of C60 to mineralization in soil. Plant uptake was generally low (∼7%), with most of the uptaken (14)C accumulating in the roots (40-47%) and smaller amounts of accumulation in the tuber (22-23%), stem (12-16%), and leaves (18-22%). Our results indicate that C60 released to the environment will not be highly bioavailable but will likely persist in soil for extended periods.

Optimizing α for better statistical decisions: a case study involving the pace-of-life syndrome hypothesis: optimal α levels set to minimize Type I and II errors frequently result in different conclusions from those using α = 0.05.

Setting optimal significance levels that minimize Type I and Type II errors allows for more transparent and well-considered statistical decision making compared to the traditional α = 0.05 significance level. We use the optimal α approach to re-assess conclusions reached by three recently published tests of the pace-of-life syndrome hypothesis, which attempts to unify occurrences of different physiological, behavioral, and life history characteristics under one theory, over different scales of biological organization. While some of the conclusions reached using optimal α were consistent to those previously reported using the traditional α = 0.05 threshold, opposing conclusions were also frequently reached. The optimal α approach reduced probabilities of Type I and Type II errors, and ensured statistical significance was associated with biological relevance. Biologists should seriously consider their choice of α when conducting null hypothesis significance tests, as there are serious disadvantages with consistent reliance on the traditional but arbitrary α = 0.05 significance level.

Negative consequences of using α = 0.05 for environmental monitoring decisions: a case study from a decade of Canada's Environmental Effects Monitoring Program.

Using the traditional α = 0.05 significance level for null hypothesis significance tests makes assumptions about relative costs of Type I vs relevant Type II errors and inflates their combined probabilities. We have examined the results of 1254 monitoring tests conducted under the Canadian Environmental Effects Monitoring (EEM) program from 1992 to 2003, focusing on how the choice of α affected the relative probabilities and implied costs of Type I and Type II errors. Using α = 0.05 resulted in implied relative costs of Type I vs Type II errors that were both inconsistent among monitoring end points and also inconsistent with the philosophy of the monitoring program. Using α = 0.05 also resulted in combinations of Type I and II error that were 15-17% larger than those for "optimal" α levels set to minimize Type I and II errors for each study, and 12% of all monitoring tests would have reached opposite conclusions had they used these optimal α levels for decision-making. Thus, if the Canadian EEM program used study-specific optimal α levels, they would reduce the incidence of relevant errors and eliminate inconsistent implied relative costs of these errors. Environmental research and monitoring programs using α = 0.05 as a decision-making threshold should re-evaluate the usefulness of this "one-size-fits-all" approach.

Perfluoroalkyl acids in sediment and water surrounding historical fire training areas at Barksdale Air Force Base.

Perfluoroalkyl acids (PFAAs) are environmentally persistent components of surfactants that consist of fully fluorinated carbon chains and a terminal sulfonate or carboxylate polar head moiety. Due to their unique amphiphilic properties, PFAAs are used in the manufacturing of products such as aqueous film forming foams (AFFF). There is cause for concern for PFAA contamination resulting from runoff and groundwater infiltration of AFFF that were used during fire training. This study analyzed water and sediment samples that were collected over a 13-month sampling period from bayous upstream and downstream of two former fire training areas located near Barksdale Air Force Base (BAFB); the occurrence and magnitude of PFAAs supported an aquatic ecological risk assessment of potential impacts of PFAAs at the site. Liquid chromatography coupled with mass spectrometry was used for determination of 6 PFAAs listed under the third Unregulated Contaminant Monitoring Rule (UCMR 3). Total PFAA concentrations in surface water and sediment samples ranged from 0 (ND) -7.1 ng/mL and 0 (ND) -31.4 ng/g, respectively. Perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) were the predominant PFAAs detected. In general, perfluorosulfonates were quantified more frequently and at higher concentrations than perfluorocarboxylates. The perfluoroalkyl chain length of PFAAs also showed significant influence on PFAA concentrations when analyzed by Spearman's rank correlation analysis. Some contamination we observed in surface water and sediment samples from reference locations could be a result of local runoff from the use of commercial products containing per- and poly-fluoroalkyl substances (PFAS), but AFFF appears to be the primary source given the close proximity of the historical fire training areas.

Compensatory indirect effects of an herbicide on wetland communities.

The direct effects of large-scale disturbances are readily studied because their effects are often apparent and result in large changes to ecosystems. Direct effects can cascade through the ecosystem, leading to indirect effects that are often subtle and difficult to detect. Managing anthropogenic disturbances, such as chemical contamination, requires an understanding of both direct and indirect effects to predict, measure, and characterize the impact. Using a replicated whole-ecosystem experiment and path analyses (assesses the effects of a set of variables on a specified outcome, similar to multiple regression), we examined the direct and indirect effects of a glyphosate-based herbicide and nutrient enrichment on wetland communities. The latter did not impact any measured endpoints. The strongest drivers of macrophyte, benthic invertebrate, and amphibian assemblages were the ephemerality and the size of wetlands, factors which were not altered by herbicide applications. The herbicide had a direct negative effect on macrophyte cover, amphibian larval abundance, and the proportion of predatory benthic invertebrates. However, both amphibians and invertebrates were positively affected by the reduction in the macrophyte cover caused by the herbicide applications. The opposing directions of the direct and indirect effects lead to no net change in either group. The compensatory dynamics observed herein highlight the need for a better understanding of indirect effects pathways to determine whether common anthropogenic disturbances alter the ecological communities in small wetland ecosystems.

Tracking neonicotinoids following their use as cotton seed treatments.

Neonicotinoids are a leading class of insecticides on the global market, accounting for nearly 25%. They are widely used in both agricultural and residential settings. Causing neuron failure by irreversibly binding to the insect nicotinic acetylcholine receptor, neonicotinoids offer broad spectrum efficacy against a variety of pests. However, because they are non-selective with regard to insect species, there has been some concern with neonicotinoid use over threats to pollinators such as honeybees, and potential indirect effects to migratory waterfowl as a result of invertebrate prey population depletion. In order to study occurrence and fate of neonicotinoids (thiamethoxam and imidacloprid), we analyzed cotton leaves on plants grown from neonicotinoid-treated seeds and corresponding soil samples between cotton rows. Neonicotinoid concentration data from cotton leaves appears to be consistent with the claim that seed treatments protect plants for 3-4 weeks; by 30 days post-planting, neonicotinoid concentrations fell, in general, to 200 ng/g or lower. This represents about a 10-fold decrease from plant concentrations at approximately 2 weeks post-planting. It was found that neonicotinoids used as seed treatments remained present in the soil for months post planting and could be available for runoff. To that end, 21 playa wetlands were sampled; 10 had at least one quantifiable neonicotinoid present, three of which were classified as grassland or rangeland playas, two were urban, and the remaining five were cropland playas. In several instances, neonicotinoid concentrations in playas exceeded EPA chronic benchmarks for aquatic invertebrates.

Temporal monitoring of perfluorooctane sulfonate accumulation in aquatic biota downstream of historical aqueous film forming foam use areas.

Perfluoroalkyl substances (PFAS) have recently received increased research attention, particularly concerning aquatic organisms and in regions of exposure to aqueous film forming foams (AFFFs). Air Force bases historically applied AFFFs in the interest of fire training exercises and have since expressed concern for PFAS contamination in biota from water bodies surrounding former fire training areas. Six PFAS were monitored, including perfluorooctane sulfonate (PFOS), in aquatic species from 8 bayou locations at Barksdale Air Force Base in Bossier City, Louisiana (USA) over the course of 1 yr. The focus was to evaluate temporal and spatial variability in PFAS concentrations from historic use of AFFF. The PFOS concentrations in fish peaked in early summer, and also increased significantly downstream of former fire training areas. Benthic organisms had lower PFOS concentrations than pelagic species, contrary to previous literature observations. Bioconcentration factors varied with time but were reduced compared with previously reported literature values. The highest concentration of PFOS in whole fish was 9349 ng/g dry weight, with 15% of samples exceeding what is believed to be the maximum whole fish concentration reported to date of 1500 ng/g wet weight. Further studies are ongoing, to measure PFAS in larger fish and tissue-specific partitioning data to compare with the current whole fish values. The high concentrations presently observed could have effects on higher trophic level organisms in this system or pose a potential risk to humans consuming contaminated fish. Environ Toxicol Chem 2017;36:2022-2029. © 2016 SETAC.

The direct and indirect effects of a glyphosate-based herbicide and nutrients on Chironomidae (Diptera) emerging from small wetlands.

Laboratory and mesocosm experiments have demonstrated that some glyphosate-based herbicides can have negative effects on benthic invertebrate species. Although these herbicides are among the most widely used in agriculture, there have been few multiple-stressor, natural system-based investigations of the impacts of glyphosate-based herbicides in combination with fertilizers on the emergence patterns of chironomids from wetlands. Using a replicated, split-wetland experiment, the authors examined the effects of 2 nominal concentrations (2.88 mg acid equivalents/L and 0.21 mg acid equivalents/L) of the glyphosate herbicide Roundup WeatherMax, alone or in combination with nutrient additions, on the emergence of Chironomidae (Diptera) before and after herbicide-induced damage to macrophytes. There were no direct effects of treatment on the structure of the Chironomidae community or on the overall emergence rates. However, after macrophyte cover declined as a result of herbicide application, there were statistically significant increases in emergence in all but the highest herbicide treatment, which had also received no nutrients. There was a negative relationship between chironomid abundance and macrophyte cover on the treated sides of wetlands. Fertilizer application did not appear to compound the effects of the herbicide treatments. Although direct toxicity of Roundup WeatherMax was not apparent, the authors observed longer-term impacts, suggesting that the indirect effects of this herbicide deserve more consideration when assessing the ecological risk of using herbicides in proximity to wetlands.

Statistical reporting deficiencies in environmental toxicology.

Null hypothesis significance testing is one of the most widely used forms of statistical testing in environmental toxicology. In this short communication, the authors show that the reporting of statistical information when using null hypothesis significance testing is frequently inadequate in environmental toxicology research. The authors demonstrate this by analyzing the statistical information reported for papers employing t tests or analyses of variance in the Environmental Toxicology section of Environmental Toxicology and Chemistry in 2010, which comprised 68% of papers published by this journal in that year. Of these papers, 60% fail to report exact p values, 85% fail to provide degrees of freedom, and 90% fail to report critical effect sizes. Statistical power was reported in only <2% of the published papers. The insufficient provision of statistical information makes interpretation of study results by reviewers and readers difficult. Consistently reporting exact p values with degrees of freedom, considering and explicitly stating biologically relevant critical effect sizes, and reporting statistical power associated with nonsignificant results would be easy to implement and would promote scientific progress in environmental toxicology through increased statistical transparency.

Setting an optimal α that minimizes errors in null hypothesis significance tests.

Null hypothesis significance testing has been under attack in recent years, partly owing to the arbitrary nature of setting α (the decision-making threshold and probability of Type I error) at a constant value, usually 0.05. If the goal of null hypothesis testing is to present conclusions in which we have the highest possible confidence, then the only logical decision-making threshold is the value that minimizes the probability (or occasionally, cost) of making errors. Setting α to minimize the combination of Type I and Type II error at a critical effect size can easily be accomplished for traditional statistical tests by calculating the α associated with the minimum average of α and ß at the critical effect size. This technique also has the flexibility to incorporate prior probabilities of null and alternate hypotheses and/or relative costs of Type I and Type II errors, if known. Using an optimal α results in stronger scientific inferences because it estimates and minimizes both Type I errors and relevant Type II errors for a test. It also results in greater transparency concerning assumptions about relevant effect size(s) and the relative costs of Type I and II errors. By contrast, the use of α = 0.05 results in arbitrary decisions about what effect sizes will likely be considered significant, if real, and results in arbitrary amounts of Type II error for meaningful potential effect sizes. We cannot identify a rationale for continuing to arbitrarily use α = 0.05 for null hypothesis significance tests in any field, when it is possible to determine an optimal α.