Effect of release herbicide on mortality, avoidance response, and growth of amphibian larvae in two forest wetlands

Effects of Release herbicide (triclopyr butoxyethyl ester, [TBEE]) on mortality, avoidance response, and growth of larval amphibians (Rana clamitans, Rana pipiens) were investigated using in situ enclosures deployed in two forest wetlands in northern Ontario, Canada. Release was applied at nominal concentrations ranging from 0.26 to 7.68 mg TBEE acid equivalents (AE)/L. No significant deleterious effects of this herbicide on larval growth were detected. However, concentration-dependent mortality and abnormal avoidance response were observed. Most mortality occurred within 96 h following treatment. Median lethal concentration (LC50) values for each species and experimental site ranged from 2.79 to 3.29 mg AE/L, while median effective concentration (EC50) values (abnormal avoidance response) ranged from 1.67 to 3.84 mg AE/L. The LC10 and EC10 endpoints approximated aqueous concentrations (0.59 mg AE/L) expected under direct aerial overspray scenarios, indicating a potential risk of impacts for a small proportion of native amphibian larvae. However, given the low frequency and limited use of this herbicide formulation in Canadian forestry, these risks are considered negligible. Changes in usage patterns would require concurrent chemical and biological monitoring of operational spray programs to accurately quantify the probability and magnitude of real-world exposures and to relate these exposure levels to concentration-response relationships including those described in this study.     

Chemical and biomonitoring to assess potential acute effects of Vision herbicide on native amphibian larvae in forest wetlands

In conjunction with operational forest herbicide spray programs in Ontario, Canada, chemical and biological monitoring studies were conducted in 51 different wetlands to quantify the probability and magnitude of contamination by a glyphosate herbicide formulation (Vision). Wetlands were classified as oversprayed, adjacent, or buffered in relation to the operational target spray blocks. Results show that vegetated buffers significantly mitigated against exposure and thus potential for acute effects. Aqueous concentrations of glyphosate in buffered wetlands were below analytical limits of quantitation (0.02 mg acid equivalent [a.e.]/L) in 14 of 16 cases, with mean concentration (0.03 +/- 0.02 mg a.e./L) significantly (p < 0.05) less than that of either adjacent (0.18 +/- 0.06 mg a.e./L) or oversprayed wetlands (0.33 +/- 0.11 mg a.e./L). Biomonitoring with caged amphibian larvae showed no significant differences among mean mortality (48 h) of either Rana pipiens (p = 0.194) or Rana clamitans larvae (p = 0.129) exposed in situ to Vision under these various wetland conditions. Percent mortality was not significantly (p = 0.05) correlated with exposure concentrations for either amphibian species tested. Results suggest that exposures typically occurring in forest wetlands are insufficient to induce significant acute mortality in native amphibian larvae.     

Multiple stress effects of Vision herbicide, pH, and food on zooplankton and larval amphibian species from forest wetlands

As part of a multiple-tier research program, interactions of the herbicide Vision (glyphosate) with two stressors, pH and food level, were examined. Effects of the formulated product Vision were tested at two test concentrations (0.75 and 1.50 mg acid equivalent/L), two pH levels (pH 5.5 and 7.5), and under high and low food concentrations. Effects of each stressor alone and in combination were examined using two common wetland taxa: Zooplankton, Simocephalus vetulus, and tadpoles (Gosner stage 25) of Rana pipiens. For S. vetulus, survival, reproduction, and development time were measured; survival was measured for R. pipiens. For both species, significant effects of the herbicide were measured at concentrations lower than the calculated worst-case value for the expected environmental concentration ([EEC], 1.40 mg acid equivalent/L). Moreover, high pH (7.5) increased the toxic effects of the herbicide on all response variables for both species even though it improved reproductive rate of S. vetulus over pH 5.5 in the absence of herbicide. Stress due to low food alone also interacted with pH 5.5 to diminish S. vetulus survival. These results support the general postulate that multiple stress interactions may exacerbate chemical effects on aquatic biota in natural systems.     

A silviculture application of the glyphosate-based herbicide VisionMAX to wetlands has limited direct effects on amphibian larvae

Herbicides are commonly used in agriculture and silviculture to reduce interspecific competition among plants and thereby enhance crop growth, quality, and volume. Internationally, glyphosate-based herbicides are the most widely used herbicides in both of these sectors. Laboratory and mesocosm studies have demonstrated that some formulations are toxic to amphibian larvae below concentrations that approximate predicted maximal or "worst-case" exposure scenarios. However, field studies have not found evidence of toxicity at these concentrations. The authors conducted a replicated field experiment involving 10 naturalized wetlands split in half with an impermeable plastic barrier to assess the direct toxicity of a glyphosate formulation commonly used in silviculture (VisionMAX?). The herbicide formulation was applied directly to the surface of one side of each wetland at one of two target aqueous exposure rates (high?=?2,880, low?=?550?μg acid equivalents [a.e.]/L), and the other side was left as an untreated control. The survival and growth of green frog larvae (Lithobates clamitans) were assessed for two years following herbicide treatment. The herbicide did not have a negative impact on survival or growth of L. clamitans larvae at either treatment level. In fact, mean larval abundance was typically greater in the treated sides than in control sides within the year of herbicide application. These results indicate that typical silviculture use of VisionMAX poses negligible risk to larval amphibians, likely because the combined effects of sorption and degradation in natural wetlands limit the exposure magnitude and duration. Environ. Toxicol. Chem. 2012; 31: 2375-2383. ? 2012 SETAC.     

Comparative effects of pH and Vision herbicide on two life stages of four anuran amphibian species

Vision, a glyphosate-based herbicide containing a 15% (weight:weight) polyethoxylated tallow amine surfactant blend, and the concurrent factor of pH were tested to determine their interactive effects on early life-stage anurans. Ninety-six-hour laboratory static renewal studies, using the embryonic and larval life stages (Gosner 25) of Rana clamitans, R. pipiens, Bufo americanus, and Xenopus laevis, were performed under a central composite rotatable design. Mortality and the prevalence of malformations were modeled using generalized linear models with a profile deviance approach for obtaining confidence intervals. There was a significant (p < 0.05) interaction of pH with Vision concentration in all eight models, such that the toxicity of Vision was amplified by elevated pH. The surfactant is the major toxic component of Vision and is hypothesized, in this study, to be the source of the pH interaction. Larvae of B. americanus and R. clamitans were 1.5 to 3.8 times more sensitive than their corresponding embryos, whereas X. laevis and R. pipiens larvae were 6.8 to 8.9 times more sensitive. At pH values above 7.5, the Vision concentrations expected to kill 50% of the test larvae in 96-h (96-h lethal concentration [LC50]) were predicted to be below the expected environmental concentration (EEC) as calculated by Canadian regulatory authorities. The EEC value represents a worst-case scenario for aerial Vision application and is calculated assuming an application of the maximum label rate (2.1 kg acid equivalents [a.e.]/ha) into a pond 15 cm in depth. The EEC of 1.4 mg a.e./L (4.5 mg/L Vision) was not exceeded by 96-h LC50 values for the embryo test. The larvae of the four species were comparable in sensitivity. Field studies should be completed using the more sensitive larval life stage to test for Vision toxicity at actual environmental concentrations.     

Multiple stressor effects of herbicide, pH, and food on wetland zooplankton and a larval amphibian

Interactions of herbicides and natural environmental stressors such as pH and food availability are poorly understood. We tested a chemical formulation of triclopyr (Release) at environmentally relevant test concentrations (0.25 and 0.50 mg L(-1)) in combination with two levels of pH (pH 5.5 and 7.5), and two levels of food availability (high and low). Population level effects of each stressor alone and in combination with the others were investigated using Simocephalus vetulus, a zooplankton species, and Rana pipiens tadpoles (Gosner stage 25), both common to forest ponds and wetlands. Herbicide treatments resulted in significant decreases in survival of both test species as well as reproduction and development time for S. vetulus at levels 5-10x below predicted worst case environmental concentrations (2.6 mg L(-1)). This laboratory study demonstrates a probable risk of toxic effects of Release herbicide which may be significantly increased by low food availability and by low pH at environmentally relevant concentrations.     

Constructed wetlands for sewage effluent treatment and mosquito larvae at two sites in subtropical Australia

This study of 2 wetlands in subtropical Australia, constructed to treat sewage effluent, examined the relationships between dips positive for mosquito larvae and water quality, operational status of the system, vegetation, and nontarget macroinvertebrates. One site is inland and the other is close to the coast. Larvae of disease vector mosquitoes were present at various times in the wetlands, especially in summer and autumn. The proportion of early instars (1st and 2nd) was greater than that of later ones (3rd and 4th). Dissolved oxygen was negatively, and temperature was positively, associated with the proportion of dips containing larvae. For the coastal site we noted that larvae were more common during draw-down of water for maintenance and also as the system started to come online. Vegetation associated with larvae included dense Typha orientalis and algae. Where there were several types of plants, such as at the coastal site, plant density and water depth were not significantly related to larval presence. Where there were several types of macroinvertebrates there were fewer dips positive for larvae. To provide water treatment capacity and minimal mosquito production we concluded that design should include a variety of plant types, discouraging low dissolved oxygen (for example, by aeration) and ongoing maintenance should be carried out in winter or spring, when mosquitoes are fewer than in summer.     

Effects of paraquat on reproduction and mortality in two generations of mice

Studies were made on the effects of paraquat on reproduction and mortality in two generations of mice (Mus musculus). Paraquat was administered in food at 0, 45, 90, and 125 mg/kg for both generations. In the first generation phase, paraquat was administered continually to mature mice beginning before pregnancy, with exposure to the F₁ to 49 days after birth. Parent (P) mice in the second generation were F₁ individuals and were continually exposed prenatal and postnatal to paraquat. Second generation control and 125 mg/kg F₂ were continued on their respective diets to 49 days after birth. Variables examined included females' age to first and second parturitions, number born per litter, offspring abnormalities, and P and offspring mortality. Lung tissue was also examined for abnormalities. No differences were observed in the females' age at the first parturition, number born per litter, or offspring abnormalities. However, paraquat treatment at 125 mg/kg produced significant (P<0.05) effects on the females' age at the second parturition, first generation P female and F₁ mortality, and P female and offspring lung tissue. Second generation mice were more resistant to paraquat poisoning than those in the first generation. The results suggest possible toxic effects that might occur with the commercial use of paraquat.     

Effects of selenium diets on growth, accumulation and antioxidant response in juvenile carp

An 8-week feeding trial was undertaken with Cyprinus carpio to determine the effects of two commercial Se diets (HSe 1.0 mg kg⁻¹ and LSe 0.25 mg kg⁻¹) on growth, accumulation and antioxidant response in juveniles at time 0, 30 and 60 days. HSe carp had higher mean weight (W) values than LSe group at 60 days and the Fulton condition factor (K) indicated good fish health for both diet groups. Among the investigated HSe tissues, kidney and liver were mainly involved in Se accumulation, whereas the Se level in muscle indicated a very low Se contamination risk for human health. Selenium accumulation levels in HSe tissues followed this order: kidney>liver>muscle. Although growth was not impaired, biochemical antioxidant indicators in liver and kidney evidenced an oxidative stress condition in HSe juveniles. Furthermore, selenium supplementation levels, higher than the one employed in this study, might worsen the antioxidant status of carp.     

Control of mosquito larvae in seasonal wetlands on a wildlife refuge using VectoMax CG

There is a great need for novel insecticides to control mosquitoes. VectoMax is a new mosquito larvicide that combines toxins from Bacillus thuringiensis subsp. israelensis (Bti) and Bacillus sphaericus (Bs), and is designed to provide extended mosquito control. We tested the initial efficacy and longevity of control of mosquitoes using one of the formulations, VectoMax CG, in a full-scale study conducted in seasonal wetlands. VectoMax CG was applied by air at 8.9 kg/ha to 3 wetlands and 3 others were untreated controls. VectoMax CG controlled Culex tarsalis through day 28 and showed activity against Aedes melanimon. Use of this dual-material, extended-action formulation could minimize inspection visits and reduce application costs compared to Bti and Bs alone, and its combination of toxins may forestall resistance development.     

Some patterns of herbicide and growth regulator intake,persistence, and distribution in sugarcane

Absorption of¹⁴C-labeled herbicides from nutrient culture solution through the roots of sugarcane plants (Saccharum spp. hybrids) resulted in three major types of distribution. Labeled residues from atrazine, ametryne, and metribuzin moved easily through the xylem to the green leaves and were deposited mainly at the leaf margins and tip. Senescence and leaf abscission removed most of the deposit from the plant. Picloram translocated rapidly into the leaves, but appeared to recycle from older to younger leaves with only small portions remaining in the senescent leaves. Asulam and pentachlorophenol (PCP) were absorbed by the roots; residues did not pass into the xylem and remained fixed in the roots.Foliar additions of labeled herbicides and growth regulators generally showed only minor absorption and translocation within the leaf. Weathering processes and volatility during a 6- to 12-week period left variable amounts of residue, characteristic of individual compounds, adsorbed at the treated sites.Published with the approval of the Director as Paper No. 355 in the Journal Series of the Experiment Station, Hawaiian Sugar Planters' Association.     

Effects of cadmium, 2,4-dichlorophenol,and pentachlorophenol on feeding,growth, and particle-size-conversion efficiency of white sucker larvae and young common shiners

Feeding rates, growth rates, and biomass conversion efficiencies were determined for white sucker larvae and young common shiners fed natural zooplankton during one week exposures to cadmium (suckers and shiners), 2,4-dichlorophenol (DCP) (shiners only), or pentachlorophenol (PCP) (shiners only). All three toxicants significantly (P < 0.01) reduced growth rates at sublethal concentrations. Growth rates were reduced up to 67 to 100% by DCP and cadmium, but the effect was smaller (a 25% reduction) for shiners. Feeding rates were not significantly affected by cadmium or DCP exposure, but shiners exposed to PCP had significantly increased feeding rates. All toxicants, therefore, reduced conversion efficiencies by >50% at sublethal concentrations. Toxicants which reduce conversion efficiency have the potential for reducing the production of top predators (large piscivores) by an amount greater than the relative effect on any one trophic level (as demonstrated in laboratory experiments) because reductions in efficiency over multiple trophic levels are cumulative.     

In Vitro effects of thes-triazine herbicide,prometryne, on the growth of terrestrial and aquatic microflora

A green alga (Chlamydomonas segnis), a cyanobacterium (Anabaena spp.), and two nitrogen-fixing bacteria (Klebsiella pneumoniae), strain M5A1 andRhizobium japonicum, strain 61A76) were separately exposed to concentrations of thes-triazine herbicide, prometryne, from 0.25–12.0 g/ml. Growth parameters observed included cell number (C. segnis), heterocyst frequency (Anabaena spp.), and generation time (K. pneumoniae andR. japonicum). A decrease in the population ofC. segnis and heterocyst frequency ofAnabaena spp. were noted after exposure to the herbicide. Full recovery was obtained in cleared cultures ofC. segnis plated on pesticide-free nutrient agar. Similar recovery was not obtained in washedAnabaena spp. cells.K. pneumoniae was relatively insensitive to the herbicide whereas the generation time ofR. japonicum, when exposed to 6.8 g/ml prometryne, was increased 3-fold compared to untreated cultures (26.25 hr vs 9.5 hr).This work was partially supported by the Natural Sciences and Engineering Research Council of Canada, Strategic Grant No. G-0930     

Effects of atrazine on embryos, larvae, and adults of anuran amphibians

We examined the effects of atrazine (0-20 mg/L) on embryos, larvae, and adult anuran amphibian species in the laboratory. Atrazine treatments did not affect hatchability of embryos or 96-h posthatch mortality of larvae of Rana pipiens, Rana sylvatica, or Bufo americanus. Furthermore, atrazine had no effect on swimming speed (measured for R. pipiens only). However, there was a dose-dependent increase in deformed larvae of all three species with increasing atrazine concentration. In adult R. pipiens, atrazine increased buccal and thoracic ventilation, indicating respiratory distress. However, because atrazine had no affect on hemoglobin, this respiratory distress was probably not indicative of reduced oxygen-carrying capacity of the blood. Frogs exposed to the highest atrazine concentration stopped eating immediately after treatment began and did not eat during the 14-d experiment. However, no decreases in mass were measured even for frogs that were not eating, probably because of compensatory fluid gain from edema. Atrazine concentrations found to be deleterious to amphibian embryos and adults are considerably higher than concentrations currently found in surface waters in North America. Therefore, direct toxicity of atrazine is probably not a significant factor in recent amphibian declines.     

Effects of the herbicide atrazine and its degradation products,alone and in combination,on phototrophic microorganisms

Toxic effects of the herbicide atrazine and four of its degradation products were determined for growth, photosynthesis, and acetylene-reducing ability of two species of green algae and three species of cyanobacteria. Atrazine was significantly more toxic than its degradation products towards the above test criteria, yielding EC₅₀ values ranging from 0.1 to 0.5 ppm (g/ml) for photosynthesis and 0.03 to 5.0 ppm for growth. Deethylated atrazine was the next most toxic with EC₅₀ values of 0.7 to 4.8, and 1.0 to 8.5 ppm for photosynthesis and growth, respectively. With deisopropylated atrazine the EC₅₀ values for the same physiological functions ranged from 3.6 to 9.3, and 2.5 to >10 ppm, respectively. Hydroxy- and diamino-atrazine were non-toxic towards most of the cultures tested. Acetylene reduction with cyanobacteria was found to be insensitive to all of the test compounds, except for atrazine, which had an EC₅₀ of 55 ± 15 ppm towardsAnabaena inaequalis. Combinations of atrazine and its monodealkylated products were tested withA. inaequalis and yielded both synergistic, antagonistic, and additive interaction responses, depending upon the actual test system employed.     

Response of biomarkers in amphibian larvae to in situ exposures in a fruit-producing region in North Patagonia, Argentina

The authors evaluated biomarker responses in caged larvae of the amphibian Rhinella arenarum in water channels during fruit production season and compared them with those elicited by a transient exposure to azinphos methyl (AzM) (0.02-2?mg/L; 4?h), the main pesticide applied in the Alto Valle region, Patagonia, Argentina, taking into account the maximum environmental concentration detected in superficial water (22.5?μg/L). The traditional biomarkers of organophosphate exposure, acetylcholinesterase (AChE) and carboxylesterase, were inhibited in tadpoles after one week of exposure in channels potentially receiving pesticide drift, whereas the antioxidant glutathione (GSH) and the detoxifying activity of GSH S-transferase (GST) were induced. In a two-week monitoring study, AChE activity was induced in larvae exposed at the agricultural site, and carboxylesterase showed an inhibition followed by return to control values, suggesting an exposure-recovery episode. Antioxidant glutathione levels were first depleted and then surpassed control levels, whereas GST activity was continuously induced. These responses were mimicked in the laboratory by 2?mg/L AzM-pulse exposure, which notably exceeds the expected environmental concentrations. The results draw attention to the complexity of responses after pesticide exposure, strongly depending on exposure time-concentration and recovery periods, among other possible factors, and support the necessity of the integrated use of biomarkers to assess exposure episodes in agricultural areas. Environ. Toxicol. Chem. 2012; 31: 2311-2317. ? 2012 SETAC.     

Effects of the hormone mimetic insecticide tebufenozide on Chironomus riparius larvae in two different exposure setups

The effects of the molting-hormone agonistic insecticide tebufenozide on larvae of the midge Chironomus riparius Meigen were tested in two different exposure setups. After static contamination of first-instar larvae the NOEC, LOEC, and LC50 values were 13.2, 17.4, and 21.14 microg/L, respectively. Semistatic exposure of fourth-instar larvae revealed a lower susceptibility of elder larvae (NOEC 30 microg/L, LOEC 60 microg/L, and LC50 81.94 microg/L). In both cases mortality was not immediate; the effects were postponed and almost exclusively linked to the processes of pupation and emergence. Pupal mortality in the semistatic exposure scheme was twice as high in males as in females during a 100 microg/L treatment. This sex-specific effect probably resulted from the endocrine activity of tebufenozide. Its detection underlines the suitability of C. riparius as a model organism for investigating effects of endocrine-disrupting chemicals in aquatic insects.