Inhibition of mitochondrial bioenergetics by carbaryl is only evident for higher concentrations -- Relevance for carbaryl toxicity mechanisms

Although pesticides have been useful in agriculture pest control, there is a considerable risk for human health and damage to ecosystems. Carbaryl is a carbamate often taken as a safe insecticide, although data on metabolic activities is still scarce, viz. mitochondrial toxicity. Therefore, it is the goal of this work to assay the compound on isolated mitochondria, a biochemical model already used with other pesticides. Mitochondria isolated from the livers of Wistar rats were assayed for bioenergetic parameters, namely mitochondrial respiration, membrane potential, membrane integrity and enzyme activities. For higher concentrations, it was observed that carbaryl has a depressive effect on mitochondrial respiration and on the generation of mitochondrial membrane potential, but with preservation of membrane integrity. A locus between Complex II and III appears particularly affected and the mitochondrial phosphorylation system relatively insensitive. Therefore, carbaryl inhibits mitochondrial respiration without affecting the phosphorylation complex. Carbaryl is toxic for mitochondria, although at concentrations higher as compared with other insecticide compounds. Mitochondrial toxicity should be excluded as one of the primary causes for carbaryl immediate toxicity, as concluded from the range of concentrations where carbaryl shows effective mitochondrial toxicity.     

Aquatic toxicity of glyphosate-based formulations: comparison between different organisms and the effects of environmental factors

Glyphosate-based herbicides (e.g. Roundup) are extensively used in the aquatic environment, but there is a paucity of data on the toxicity of the formulated products and the influences by environmental factors. In this study, the acute toxicity of technical-grade glyphosate acid, isopropylamine (IPA) salt of glyphosate, Roundup and its surfactant polyoxyethylene amine (POEA) to Microtox bacterium (Vibrio fischeri), microalgae (Selenastrum capricornutum and Skeletonema costatum), protozoa (Tetrahymena pyriformis and Euplotes vannus) and crustaceans (Ceriodaphnia dubia and Acartia tonsa) was examined and the relative toxicity contributions of POEA to Roundup were calculated. The effects of four environmental factors (temperature, pH, suspended sediment and algal food concentrations) on the acute toxicity of Roundup to C. dubia were also examined. Generally, the toxicity order of the chemicals was: POEA>Roundup>glyphosate acid>IPA salt of glyphosate, while the toxicity of glyphosate acid was mainly due to its high acidity. Microtox bacterium and protozoa had similar sensitivities towards Roundup toxicity (i.e. IC50 from 23.5 to 29.5 mg AE/l). In contrast, microalgae and crustaceans were 4-5 folds more sensitive to Roundup toxicity than bacteria and protozoa. Except photosynthetic microalgae, POEA accounted for more than 86% of Roundup toxicity and the toxicity contribution of POEA was shown to be species-dependent. Increase in pH (6-9) and increase of suspended sediment concentration (0-200 mg/l) significantly increased the toxicity of Roundup to C. dubia, but there were no significant effects due to temperature change and food addition.     

Bioaccumulation of glyphosate and its formulation Roundup Ultra in Lumbriculus variegatus and its effects on biotransformation and antioxidant enzymes

The bioaccumulation potential of glyphosate and the formulation Roundup Ultra, as well as possible effects on biotransformation and antioxidant enzymes in Lumbriculus variegatus were compared by four days exposure to concentrations between 0.05 and 5 mg L⁻¹ pure glyphosate and its formulation. Bioaccumulation was determined using ¹⁴C labeled glyphosate. The bioaccumulation factor (BCF) varied between 1.4 and 5.9 for the different concentrations, and was higher than estimated from log P_ow. Glyphosate and its surfactant POEA caused elevation of biotransformation enzyme soluble glutathione S-transferase at non-toxic concentrations. Membrane bound glutathione S-transferase activity was significantly elevated in Roundup Ultra exposed worms, compared to treatment with equal glyphosate concentrations, but did not significantly differ from the control. Antioxidant enzyme superoxide dismutase was significantly increased by glyphosate but in particular by Roundup Ultra exposure indicating oxidative stress. The results show that the formulation Roundup Ultra is of more ecotoxicological relevance than the glyphosate itself.     

Influence of glyphosate and its formulation (Roundup) on the toxicity and bioavailability of metals to Ceriodaphnia dubia

This study examined the toxicological interaction between glyphosate (or its formulation, Roundup) and several heavy metals to a freshwater cladoceran, Ceriodaphnia dubia. We demonstrated that all binary combinations of Roundup and metals (Cd, Cu, Cr, Ni, Pb, Se and Zn) exhibited "less than additive" mixture toxicity, with 48-h LC50 toxic unit > 1. Addition of glyphosate alone could significantly reduce the acute toxicity of Ag, Cd, Cr, Cu, Ni, Pb and Zn (but not Hg and Se). The ratio between glyphosate and metal ions was important in determining the mitigation of metal toxicity by glyphosate. A bioaccumulation study showed that in the presence of glyphosate the uptake of some metals (e.g. Ag) was halted but that of others (e.g. Hg) was increased significantly. Therefore, our study strongly suggests that glyphosate and its commercial formulations can control the toxicity as well as the bioavailability of heavy metals in aquatic ecosystems where both groups of chemicals can co-occur.     

Environmental fate and non-target impact of glyphosate-based herbicide (Roundup) in a subtropical wetland

Mai Po Nature Reserve (Hong Kong) is an internationally important wetland for waterbirds. Roundup, a formulation based on glyphosate, has been used to control the widespread weeds within the reserve for many years but the fate and non-target impact of the herbicide is unknown. To fill this knowledge gap, we applied Roundup by hand-held sprayer to an estuarine and a freshwater pond in the dry season of year 2002. The surface water and sediment were sampled routinely for glyphosate concentrations following one month of application. In situ bioassays using local edible fish species were performed along with the herbicide application. Up to 52% of glyphosate in the surface water was transported to the unapplied regions by wind-driven current in the estuarine pond at 1 DPT (day post treatment). For both ponds, glyphosate concentrations in the water decreased rapidly after 1-3 DPT, but then decreased gradually over time. Both physical adsorption to the bottom sediments and microbial degradation are thought to contribute to these decreases. Interestingly, the persistence of glyphosate in the freshwater pond was longer than in the estuarine system, which is likely due to the considerably higher concentrations of chelating metals (i.e. Cu and Fe) present in the sediment (4.5 and 11-fold higher, respectively) which potentially reduced the bioavailability of glyphosate to the microbial decomposers. Lastly, fishes used in the in situ bioassays (both in applied and unapplied areas) showed similar survival rates, indicating that the use of Roundup at the provided application rate posed no serious hazard.     

Disruption of hepatic mitochondrial bioenergetics is not a primary mechanism for the toxicity of methoprene - relevance for toxicological assessment

Methoprene (isopropyl(2E,4E)-11-methoxy-3,7,11-trimethyl-2,4-dodecadienoate) is an insect growth regulator generally used to control insect populations by preventing insect maturation. So far, the effects of the insecticide on mitochondrial bioenergetics were not investigated. In the present work, liver mitochondria from Wistar rats were isolated and features of mitochondrial physiology were characterized in the presence of methoprene. High concentrations of methoprene, in the range of 40-100 nmol/mg of protein could decrease the transmembrane electric potential (Delta Psi) developed by mitochondria and, at the highest concentration, methoprene prevented complete Delta Psi repolarization after ADP addition. The effect was more evident using succinate than with ascorbate+TMPD as substrate. State 3 respiration was approximately 60% inhibited by 80 nmol of methoprene/mg of protein, while state 4 respiration, within the same range of methoprene concentrations, showed a slight increase, when both glutamate-malate and succinate were used as substrates. Additionally, FCCP-stimulated respiration was inhibited to an extent comparable to the effect on state 3, which suggests an interaction of methoprene with the respiratory chain, more evident with glutamate/malate as substrate. The activity of complex I (NADH-ubiquinone oxidorreductase) and that of the segment comprehending complexes II and III (succinate-cytochrome c reductase) were decreased in the presence of methoprene (approximately 60% and 85% of inhibition, respectively, with 300 nmol of methoprene/mg of protein), while the activities of cytochrome c oxidase and ATPase do not seem to be affected. Furthermore, the action of methoprene on the mitochondrial permeability transition was also studied, showing that the insecticide (in the range of 30-80 nmol mg(-1) of protein) decreases the susceptibility of liver mitochondria to the opening of the transition pore, even in non-energized mitochondria. These results lead to the conclusion that methoprene interference with hepatic mitochondrial function occurs only for high concentrations, which implies that the noxious effects of the insecticide reported for a number of non-target organisms are not fully attributable to mitochondrial effects. Therefore, it seems that mitochondrial activity does not represent the primary target for methoprene toxic action.     

In vitro cytotoxicity assessment of roundup (glyphosate) in L-02 hepatocytes

The goal of the present study was to elucidate the in vitro cytotoxicity of Roundup and to reveal the possible related mechanisms in L-02 hepatocytes. By detecting reactive oxygen species (ROS) production, glutathione (GSH)/superoxide dismutase (SOD) levels, mitochondrial permeability transition pore (PTP) open rate, apoptosis-inducing factor (AIF) release, intracellular Ca²⁺ concentration, and alanine aminotransferease (ALT)/aspartate aminotransferase (AST) leakage, we determined that Roundup induced anti-oxidant system inhibition, mitochondria damage, DNA damage, membrane integrity and permeability changes, and apoptosis in L-02 hepatocytes. By revealing the mechanistic insights of Roundup-induced cytotoxicity, our results are valuable for the design of preventive and therapeutic strategies for the occupational population exposed to Roundup and other pesticides.     

Acute and chronic toxicity of Roundup Weathermax and Ignite 280 SL to larval Spea multiplicata and S. bombifrons from the Southern High Plains, USA

Pesticides have been implicated in widespread amphibian declines. We assessed acute and chronic toxicity of two widely used herbicides to larval New Mexico (Spea multiplicata) and Plains (S. bombifrons) spadefoots from cropland and native grassland playas. Roundup WeatherMAX^® (WM) toxicity estimates (48- and 216-h LC₅₀; 48-h LC₁) for both species were similar to environmental concentrations expected from accidental overspray. Chronic (30-day) exposure to WM at predicted environmental concentrations (2.0 and 2.8 mg glyphosate acid equivalents/L) reduced survival of both species. Ignite^® 280 SL (IG) toxicity estimates (48-h LC₅₀ and LC₁) for both species were above predicted environmental concentrations of 1.0 mg glufosinate/L. Chronic exposure to predicted environmental concentrations of IG did not reduce survival of either species. Toxicity test results suggest that at predicted environmental concentrations IG would not cause extensive mortalities among larval New Mexico and Plains spadefoots. However, WM may cause extensive mortality among larvae of these species.     

Assessment of toxicity of a glyphosate-based formulation using bacterial systems in lake water

A new Aeromonas bioassay is described to assess the potential harmful effects of the glyphosate-based herbicide, Roundup^®, in the Albufera lake, a protected area near Valencia. Viability markers as membrane integrity, culturability and β-galactosidase production of Aeromonas caviae were studied to determine the influence of the herbicide in the bacterial cells. Data from the multifactor analysis of variance test showed no significant differences (P > 0.05) between A. caviae counts of viability markers at the studied concentrations (0, 50 and 100 mg l⁻¹ of glyphosate).

The effects of Roundup^® on microbial biota present in the lake were assessed by measuring the number of indigenous mesophilic Aeromonas in presence of different amounts of the herbicide at 0, 50 and 100 mg l⁻¹ of glyphosate. In samples containing 50 and 100 mg l⁻¹ of glyphosate a significant (P < 0.05) increase in Aeromonas spp. counts and accompanying flora was observed.

The acute toxicity of Roundup^® and of Roundup^® diluted with Albufera lake water to Microtox^® luminescent bacterium (Vibrio fischeri) also was determined. The EC₅₀ values obtained were 36.4 mg l⁻¹ and 64.0 mg l⁻¹ of glyphosate respectively. The acidity (pH 4.5) of the herbicide formulation was the responsible of the observed toxicity.     

Effects of glyphosate on the non-target leaf beetle Cerotoma arcuata (Coleoptera: Chrysomelidae) in field and laboratory conditions

This study aimed to assess the glyphosate application effects on the Cerotoma arcuata Oliver (Coleoptera: Chrysomelidae) population in glyphosate-resistant soybean crops. Field studies were conducted with glyphosate and the insecticide endosulfan to observe the effects of these pesticides on C. arcuata, on its damages in the crop and on the populations of natural enemies in glyphosate-resistant soybean crops. Moreover, the lethal and behavioral sublethal response of C. arcuata to glyphosate and endosulfan was conducted in the laboratory. The results of the field and laboratory experiments showed that glyphosate caused moderate toxicity and high irritability in C. arcuata and that endosulfan caused high toxicity and irritability. Therefore, the direct effect of glyphosate on C. arcuata was negative and does not explain the population increases of this pest in glyphosate-resistant soybean. However, the glyphosate also decreased the density of predators. Thus, the negative effect of glyphosate on the predators may be related to population increases of C. arcuata in glyphosate-resistant soybean crops, however, more studies are needed to better evidence this relationship. This study suggests that glyphosate can impact other non-target organisms, such as herbivorous insects and natural enemies and that the use of this herbicide will need to be carefully stewarded to prevent potential disturbances in beneficial insect communities in agricultural systems.     

Cadmium- and calcium-mediated toxicity in rainbow trout (Oncorhynchus mykiss) in vivo: interactions on fitness and mitochondrial endpoints

Rainbow trout were exposed to sublethal waterborne Cd (5 and 10 μg L⁻¹) and dietary Ca (60 mg g⁻¹), individually and in combination, for 30 d to elucidate the interactive effects and evaluate the toxicological significance of mitochondrial responses to these cations in vivo. Indices of fish condition and mortality were measured and livers, centers of metabolic homeostasis, were harvested to assess mitochondrial function and cation accumulation. All indices of condition assessed (body weight, hepatosomatic index and condition factor) were reduced in all the treatment groups. Mortality occurred in the Cd-exposed groups with dietary Ca partly protecting against and enhancing it in the lower and higher Cd exposure, respectively. State 3 mitochondrial respiration was inhibited by 30%, 35% and 40% in livers of fish exposed to Ca, Cd and Cd + Ca, respectively, suggesting reduced ATP turnover and/or impaired substrate oxidation. While the phosphorylation efficiency was unaffected, state 4 and state 4+ (+ oligomycin) respirations were inhibited by all the exposures. Mitochondrial coupling was reduced and transiently restored denoting partially effective compensatory mechanisms to counteract Cd/Ca toxicity. The respiratory dysfunction was associated with accumulation of both Cd and Ca in the mitochondria. Although fish that survived acute effects of Cd and Ca exposure apparently made adjustments to energy generation such that liver mitochondria functioned more efficiently albeit at reduced capacity, reduced fitness was persistent possibly due to increased demands for maintenance and defense against toxicity. Overall, interactions between Cd and Ca on condition indices and mitochondrial responses were competitive or cooperative depending on exposure concentrations and duration.     

Dissipation of glyphosate and aminomethylphosphonic acid in water and sediment of two Canadian prairie wetlands

Glyphosate [N-(phosphonomethyl)glycine] is the active ingredient of several herbicide products first registered for use in 1974 under the tradename Roundup. The use of glyphosate-based herbicides has increased dramatically over the last two decades particularly in association with the adoption of glyphosate-tolerant crops. Glyphosate has been detected in a range of surface waters but this is the first study to monitor its fate in prairie wetlands situated in agricultural fields. An ephemeral wetland (E) and a semi-permanent wetland (SP) were each divided into halves using a polyvinyl curtain. One half of each wetland was fortified with glyphosate with the added mass simulating an accidental direct overspray. Glyphosate dissipated rapidly in the water column of the two prairie wetlands studied (DT(50) values of 1.3 and 4.8 d) which may effectively reduce the impact of exposure of aquatic biota to the herbicide. Degradation of glyphosate to its major metabolite aminomethylphosphonic acid (AMPA) and sorption of the herbicide to bottom sediment were more important pathways for the dissipation of glyphosate from the water column than movement of the herbicide with infiltrating water. Presently, we are not aware of any Canadian guidelines for glyphosate residues in sediment of aquatic ecosystems. Since a substantial portion of glyphosate entering prairie wetlands will become associated with bottom sediments, particularly in ephemeral wetlands, guidelines would need to be developed to assess the protection of organisms that spend all or part of their lifecycle in sediment.     

In vivo evaluation of three biomarkers in the mosquitofish (Gambusia yucatana) exposed to pesticides

In this study, the acute toxicity and the in vivo effects of commercial chlorpyrifos, carbofuran and glyphosate formulations on cholinesterase (ChE), glutathione S-transferase (GST) and lactate dehydrogenase (LDH) activities of the mosquitofish (Gambusia yucatana) were investigated. In a first phase of the study, head and muscle ChE were characterized with different substrates (acetylthiocholine iodide, s-butyrylthiocholine iodide and propionylthiocholine iodide) and the selective inhibitors eserine hemisulfate, 1,5-bis(4-allyldimethylammoniumphenyl)-pentan-3-one dibromide (BW284C51), and N,N'-diisopropylphosphorodiamic acid (iso-OMPA). The results obtained suggest that the enzyme present in both head and muscle of G. yucatana is mainly acetylcholinesterase (AChE). Acute toxicity was evaluated by exposing fish to several concentrations of single pesticides and of a mixture of chlorpyrifos/glyphosate. LC50 values were determined after 96 h of exposure, except in the case of carbofuran for which LC50 was calculated after 24 h since almost all the fish died within this period. LC50 values were 0.085 mg/l for chlorpyrifos, 17.79 mg/l for glyphosate, 0.636 mg/l for carbofuran and 0.011 mg/l for the chlorpyrifos/glyphosate mixture. A Toxic Unit approach was used to compare the toxicity of chlorpyrifos and glyphosate when occurring in a mixture with their toxicities as single compounds. Synergistic effects of chlorpyrifos and glyphosate when present in a mixture were found. At the end of each bioassay (24 h for carbofuran, 96 for the other substances/mixture), effects on biomarkers were analyzed. Muscle LDH activity was not altered by any of the three pesticides tested. Gill GST activity was significantly inhibited (40%) by carbofuran after 24 h of exposure to concentrations equal or higher than 0.06 mg/l. ChE muscle and head activity were significantly inhibited (50% and 30%, respectively) by carbofuran at concentrations equal or higher than 0.25 mg/l. Chlorpyrifos induced a significant inhibition of both muscle and head ChE (80% and 50%, respectively) after 96 h of exposure to concentrations equal or higher than 0.05 mg/l. Carbofuran did not induce significant alterations of fish ChE. The ChE EC50 determined for chlorpyrifos/glyphosate mixture (0.070 mg/l) was higher than the correspondent value calculated for chlorpyrifos alone (0.011 mg/l) suggesting an antagonistic effect of glyphosate on ChE inhibition by chlorpyrifos. ChE activity of G. yucatana seems to be a good biomarker to diagnose the exposure of wild populations of this species exposed to anticholinesterase pesticides.     

Dissipation of glyphosate and aminomethylphosphonic acid in water and sediment of two Canadian prairie wetlands

Glyphosate [N-(phosphonomethyl)glycine] is the active ingredient of several herbicide products first registered for use in 1974 under the tradename Roundup. The use of glyphosate-based herbicides has increased dramatically over the last two decades particularly in association with the adoption of glyphosate-tolerant crops. Glyphosate has been detected in a range of surface waters but this is the first study to monitor its fate in prairie wetlands situated in agricultural fields. An ephemeral wetland (E) and a semi-permanent wetland (SP) were each divided into halves using a polyvinyl curtain. One half of each wetland was fortified with glyphosate with the added mass simulating an accidental direct overspray. Glyphosate dissipated rapidly in the water column of the two prairie wetlands studied (DT₅₀ values of 1.3 and 4.8 d) which may effectively reduce the impact of exposure of aquatic biota to the herbicide. Degradation of glyphosate to its major metabolite aminomethylphosphonic acid (AMPA) and sorption of the herbicide to bottom sediment were more important pathways for the dissipation of glyphosate from the water column than movement of the herbicide with infiltrating water. Presently, we are not aware of any Canadian guidelines for glyphosate residues in sediment of aquatic ecosystems. Since a substantial portion of glyphosate entering prairie wetlands will become associated with bottom sediments, particularly in ephemeral wetlands, guidelines would need to be developed to assess the protection of organisms that spend all or part of their lifecycle in sediment.     

Toxicity of the herbicide glyphosate to Chordodes nobilii (Gordiida, Nematomorpha)

Nematomorpha (horsehair worms) is a poorly known group of worm-like animals similar to nematodes. Adults are free-living and reproduction takes place in freshwater environments, where preparasitic larvae undergo development. All species have a parasitic juvenil stage and infection may result in the host's death, insects being the most frequent host. Most of the life cycle occurs in freshwater environments, which are often contaminated by different pollutants. Based on the lack of information on the toxicity of herbicides to horsehair worms, the objective of this study is to evaluate the effect of different concentrations of glyphosate (technical grade and formulated product) on Chordodes nobilii (Gordiida, Nematomorpha). Bioassays were performed with embryos and larvae (preparasitic stages), and adults (postparasitic stage). Test organisms were exposed for a short period of time to concentrations ranging between 0.1 and 8 mga.e.l(-1) of glyphosate (technical and formulated). Although embryo development was not inhibited, there was a significant decrease in the infective capacity of larvae derived from eggs that had been exposed to >or= 0.1mg/l. Similar results were obtained for directly exposed larvae. No differences in toxicity were detected between the active ingredient and formulated product. Adult exposed for 96 h to 1.76 mgl(-1) formulated Gly shown a mortality of 50%. Results indicate that C. nobilii is affected at glyphosate concentrations lower than those expected to be found in freshwater environments and those specified in the legislation.     

The effect of glyphosate on the growth and competitive effect of perennial grass species in semi-natural grasslands

Biodiversity within European semi-natural biotopes in agro-ecosystem is declining, and herbicide drift from neighbouring fields is considered as an important factor for the decline. The aim of the present study was to investigate whether the growth and competitive interactions in a model system of two perennial grass species, Festuca ovina and Agrostis capillaris, are affected by sub-lethal doses of glyphosate in field margins. In a glasshouse experiment with ample nitrogen, the interspecific competitive interactions were found to be significantly affected by glyphosate; the competitive effect of F. ovina on A. capillaris increased and the competitive effect of A. capillaris on F. ovina decreased with increasing doses of glyphosate. Furthermore, the importance of interspecific competition increased with the glyphosate dose. The results of the study of competitive interactions are in agreement with the observed plant community dynamics at the field site where F. ovina was found to be more dominant in plots treated with a relatively high dose of glyphosate. Importantly, the effects of glyphosate on the plant community dynamics critically depended on the effect of glyphosate on the plant competitive interactions. The study concludes that the current practice in the environmental risk assessment of non-target effects of herbicides, where single species are tested in the greenhouse, may be inadequate for assessing the effect of herbicides in semi-natural plant communities. The presented methods can be used for assessing the importance of competitive interactions for the sensitivity of non-target plants to herbicides in risk assessment.     

Evaluation of the cytotoxic effects of glyphosate herbicides in human liver,lung, and nerve

Glyphosate-based herbicides are broad-spectrum pesticides widely used in the world, which is considered a highly safe pesticide due to their target specificity, but recently, there has been an ongoing controversy regarding their carcinogenicity and possible side effects of glyphosate on human health. Commercial glyphosate-based herbicides (GBHs) consist of declared active ingredient (glyphosate salts) and a number of formulants such as ethoxylated formulants (4130®, 3780^®, and A-178^®). The aim of our study is to investigate whether the toxicity of GBHs is related to formulants. The effects of GBHs on human health were studied at the cellular level based on their toxicity to liver, lungs and nerve tissue. The inhibitory toxicity to cell viability by GBHs was examined with cell-based systems using three human cell lines: HepG2, A549, and SH-SY5Y. Data obtained showed that all tested ethoxylated formulants and their mixtures with declared active ingredient glyphosate isopropylamine salt (GP) have significant inhibitory effect on cell proliferation, while the declared active ingredient has no significant toxicity. Our study demonstrates that the toxic effect of GBH is primarily due to the use of formulants. This result suggests that GP is relatively safe and a new approach for the assessment of toxicity should be made.     

Glyphosate: environmental contamination,toxicity and potential risks to human health via food contamination

Glyphosate has been the most widely used herbicide during the past three decades. The US Environmental Protection Agency (EPA) classifies glyphosate as ‘practically non-toxic and not an irritant’ under the acute toxicity classification system. This classification is based primarily on toxicity data and due to its unique mode of action via a biochemical pathway that only exists in a small number of organisms that utilise the shikimic acid pathway to produce amino acids, most of which are green plants. This classification is supported by the majority of scientific literature on the toxic effects of glyphosate. However, in 2005, the Food and Agriculture Organisation (FAO) reported that glyphosate and its major metabolite, aminomethylphosphonic acid (AMPA), are of potential toxicological concern, mainly as a result of accumulation of residues in the food chain. The FAO further states that the dietary risk of glyphosate and AMPA is unlikely if the maximum daily intake of 1 mg kg^?1 body weight (bw) is not exceeded. Research has now established that glyphosate can persist in the environment, and therefore, assessments of the health risks associated with glyphosate are more complicated than suggested by acute toxicity data that relate primarily to accidental high-rate exposure. We have used recent literature to assess the possible risks associated with the presence of glyphosate residues in food and the environment.     

Transport and attenuation of dissolved glyphosate and AMPA in a stormwater wetland

Glyphosate is an herbicide used widely and increasingly since the early 1990s in production of many crops and in urban areas. However, knowledge on the transport of glyphosate and its degradation to aminomethylphosphonic acid (AMPA) in ecosystems receiving urban or agricultural runoff is lacking. Here we show that transport and attenuation of runoff-associated glyphosate and AMPA in a stormwater wetland differ and largely vary over time. Dissolved concentrations and loads of glyphosate and AMPA in a wetland receiving runoff from a vineyard catchment were assessed during three consecutive seasons of glyphosate use (March to June 2009, 2010 and 2011). The load removal of glyphosate and AMPA by the wetland gradually varied yearly from 75% to 99%. However, glyphosate and AMPA were not detected in the wetland sediment, which emphasises that sorption on the wetland vegetation, which increased over time, and biodegradation were prevailing attenuation processes. The relative load of AMPA as a percentage of total glyphosate increased in the wetland and ranged from 0% to 100%, which indicates the variability of glyphosate degradation via the AMPA pathway. Our results demonstrate that transport and degradation of glyphosate in stormwater wetlands can largely change over time, mainly depending on the characteristics of the runoff event and the wetland vegetation. We anticipate our results to be a starting point for considering degradation products of runoff-associated pesticides during their transfer in wetlands, in particular when using stormwater wetlands as a management practice targeting pesticide attenuation.     

Development of zinc bioavailability and toxicity for the springtail Folsomia candida in an experimentally contaminated field plot

The influence of outdoor exposure conditions and ageing of contamination on the toxicity of zinc was investigated for the springtail Folsomia candida to evaluate the validity of a standardised soil toxicity test. In three successive years, animals were incubated in an experimentally contaminated field plot. During the first months after construction of the test field, total zine concentrations of the soil decreased rapidly due to leaching of excess zinc with rainwater, while increased sorption of the remaining residues resulted in a reduced bioavailability of the metal. Although variation between replicates was substantial, the EC50s for the effect of zinc on reproduction of F. candida determined in the field experiments differed by less than a factor of two from effect concentrations obtained in laboratory tests in which the same soil was used. Expression of the EC50s on the basis of water soluble zinc allowed for a comparison with effect concentrations estimated for other soil types. EC50s were comparable with literature data, which indicates that bioavailability of zinc is the main factor determining toxicity for F. candida. It is concluded that laboratory based toxicity data are suitable to predict effects of zinc for F. candida under outdoor conditions, provided that the bioavailability of zinc is determined accurately using water soluble concentrations.