Toxicity Ranking and Toxic Mode of Action Evaluation of Commonly Used Agricultural Adjuvants on the Basis of Bacterial Gene Expression Profiles

The omnipresent group of pesticide adjuvants are often referred to as “inert” ingredients, a rather misleading term since consumers associate this term with “safe”. The upcoming new EU regulation concerning the introduction of plant protection products on the market (EC1107/2009) includes for the first time the demand for information on the possible negative effects of not only the active ingredients but also the used adjuvants. This new regulation requires basic toxicological information that allows decisions on the use/ban or preference of use of available adjuvants. In this study we obtained toxicological relevant information through a multiple endpoint reporter assay for a broad selection of commonly used adjuvants including several solvents (e.g. isophorone) and non-ionic surfactants (e.g. ethoxylated alcohols). The used assay allows the toxicity screening in a mechanistic way, with direct measurement of specific toxicological responses (e.g. oxidative stress, DNA damage, membrane damage and general cell lesions). The results show that the selected solvents are less toxic than the surfactants, suggesting that solvents may have a preference of use, but further research on more compounds is needed to confirm this observation. The gene expression profiles of the selected surfactants reveal that a phenol (ethoxylated tristyrylphenol) and an organosilicone surfactant (ethoxylated trisiloxane) show little or no inductions at EC20 concentrations, making them preferred surfactants for use in different applications. The organosilicone surfactant shows little or no toxicity and good adjuvant properties. However, this study also illustrates possible genotoxicity (induction of the bacterial SOS response) for several surfactants (POEA, AE, tri-EO, EO FA and EO NP) and one solvent (gamma-butyrolactone). Although the number of compounds that were evaluated is rather limited (13), the results show that the used reporter assay is a promising tool to rank commonly used agricultural adjuvants based on toxicity and toxic mode of action data

Comparative toxicity of glyphosate-based herbicides: Aqueous and sediment porewater exposures

Glyphosate-based herbicides are widely used for aquatic weed control. However, their aquatic toxicity data, especially those on sediment, are relatively scarce. In this study,the water-only acute toxicity of three formulations based on glyphosate (Rodeo, Roundup Biactive, and Roundup) were compared using a water-column organism (cladoceran: Ceriodaphnia dubia) and a benthic organism (amphipod: Hyalella azteca). In addition, Roundup Biactive and Roundup were spiked into a clean sediment which was amended with appropriate amounts of peat moss to study the effect of different organic carbon levels (0, 0.4, 1.2, and 2.1\%) on their sediment toxicity, with C dubia exposed to overlying Water or porewater prepared from the contaminated sediments. Results showed that the toxicity based on 48-h LC50s for the three herbicides in the water-only tests was Roundup (1.5-5.7 mg L-1) > Roundup Biactive (82-120 mg L-1) > Rodeo (225-415 mg L-1), and H. azteca was generally more sensitive than C dubia to these herbicides. Toxicity differences between formulations were due to the different surfactant components in these herbicides. From the porewater toxicity tests, Roundup Biactive (340 mg kg(-1)) and Roundup (244 mg kg(-1)) were similarly toxic in the sediment tests at 0\% organic carbon, indicating that the surfactants in Roundup were considerably more adsorptive than those in Roundup Biactive to the sediment of the same organic carbon. Also, an increase in organic carbon significantly decreased the toxicity of Roundup in sediment, but not for Roundup Biactive. Sediment-porewater partitioning of glyphosate was found to be influenced by sediment organic carbon (i.e., glyphosate adsorption increased with sediment organic carbon)

Temperature influences on the accumulation and elimination of mercury in a freshwater cladoceran, Daphnia magna

Temperature is an important environmental variable affecting the physiology and metabolism of aquatic invertebrates and can potentially affect the rate and pathway of the uptake and elimination of contaminants. In this study, we studied the effects of the ambient temperature on the uptake (from water and food) and elimination of inorganic mercury [Hg(II)] and methymercury (MeHg) in a freshwater cladoceran, Daphnia magna, in the laboratory. At different temperatures (i.e., 14, 19 and 24degreesC), the assimilation efficiencies of both Hg species from ingested alga were not significantly different while the dissolved uptake rates were 32 and 73\% lower at WC than at 24degreesC for Hg(II) and MeHg, respectively. The reduced uptake rates of Hg(II) at WC could be adequately explained by the reduced filtration rate (40\% reduction), but for MeHg, the reduced filtration rate could not completely explain reduction in MeHg uptake rate. Despite the elimination rates of both Hg compounds not being affected by the temperature, the relative importance of different routes of Hg loss (i.e., excretion, egestion, molting and reproduction) was significantly different at various temperatures. The relative importance of excretion to MeHg loss increased from 24 to WC (i.e., 52 to 85\% of Hg loss) while that of reproduction to MeHg loss decreased from 43 to 11\% simultaneously. Using a kinetic model, we showed that the fraction of MeHg accumulated in the daphnids coming from the dietary phase was higher at lower temperature, while there was increased accumulation of both Hg(II) and MeHg in the daphnids at higher temperatures. Nevertheless, the trophic transfer potentials for both Hg species in this algae-daphnids food chain were not influenced by the temperature. (C) 2004 Elsevier B.V. All rights reserved

Maternal transfer efficiency and transgenerational toxicity of methylmercury in Daphnia magna

We examined maternal transfer efficiency, retention by subsequent generations, and transgenerational toxicity of methylmercury (CH3Hg or MeHg) in a population of freshwater zooplankton (Daphnia Magna). The effect of dietary MeHg residence time in the daphnids on the efflux system also was quantified. After ingesting a relatively high dosage of MeHg, D. Magna exhibited a reduction of live neonates and an increase of undeveloped eggs (or embryos), which reflected the sublethal toxicity of MeHg. The daily maternal transfer efficiency of MeHg to both reproductive outputs ranged from 0.42 to 4.9\% over different ages of the parental daphnids, which was dependent on the daily reproductive output. During the lifetime of D. Magna, reproduction contributed to 10.8\% +/- 1.74\% (n = 3) SD of total MeHg loss from the parental daphnids. The percentage of MeHg retention by the second generation (F-1) of D. Magna (40-60\%) was generally higher than that by the parental generation (F-0; similar to25\%) after 20 d of depuration. Methylmercury imposed sublethal toxicity to the F-0 and F-1 generations, but a smaller effect was observed on the F-2 generation. Because of the very low MeHg body burden in the subsequent generations, we hypothesized that factors other than MeHg, such as nutritional deficiency in the offspring contributed to the transgenerational toxicity. Different MeHg residence times did not significantly affect the efflux rate of MeHg but did significantly affect the relative importance of reproduction as the elimination pathway for MeHg. Based on the MeHg body burden of neonates, we estimated that MeHg took 2.5 to 3.0 d to be optimally transferred from assimilation (e.g., gut) to the site of egg development (e.g., brood chamber) in D. Magna. Our study demonstrated that maternal transfer of MeHg in freshwater zooplankton is an important predictor of MeHg concentration in their offspring and is a time-dependent and highly dynamic process

Multigenerational acclimation of Daphnia magna to mercury: Relationships between biokinetics and toxicity

We examined the effects of multigenerational exposure of mercury (Hg) on Hg toxicity and biokinetics in a population of Daphnia magna. After chronic Hg exposure at 3.8 mu g Hg/L, the first generation (F-0) adults had an elevated 24-h median lethal concentration (LC50) of Hg (76 mu g/L) when compared to the control adults (56 mu g/L). The dissolved influx rate of Hg was depressed significantly in the H.-treated adults, which was accompanied by a reduced ingestion rate and enhanced induction of metallothionein-like proteins (MTLP). The second-generation (F-1) juveniles originating from the control and exposed lines had no major differences in these parameters (except the dietary assimilation efficiency). Recovery from Hg stress enhanced the vulnerability of F-1 adults to Hg toxicity. with a reduced 48-h LC50 (44 mu g/L) and a decreased concentration of MTLP (80\% of control). Nevertheless, Hg-treated F-1 adults had similar tolerance (in terms of LC50s) as the control line, indicating that D. magna acclimated to Hg stress after the first generation of exposure. No major difference occurred in the Hg biokinetics and toxicity among different groups of F-2 daphnids. However. the F-2 neonates produced by the H-treated F-1 adults had much higher 48-h LC50 (149 mu g/L) and MTLP concentration (148\% of control) when there was continuous Hg exposure after birth. We concluded that acclimation to Hg stress occurred quickly in D. magna, though animals recovering from Hg stress were more vulnerable to Hg toxicity. Both ingestion rate and MTLP may not be good biomarkers of Hg stress in the field, because acclimation can be achieved through multigenerational exposure to elevated Hg concentrations

Influences of maternal exposure on the tolerance and physiological performance of Daphnia magna under mercury stress

We examined the tolerance development to mercury (Hg) by a population of freshwater zooplankton (Daphnia magna) with different pre-exposure histories to Hg. The growth and reproductive performance of the F, offspring as affected by the maternal (F,) and offspring (F,) exposures was quantified. The F-0 daphnids exposed to 2.5 and 25 nM of Hg for 4 d and followed by 4 d of depuration had elevated levels of Mg and metal lothionein-like proteins (MTLPs), as well as higher tolerance to Hg toxicity than the control daphnids. The higher Hg tolerance may be attributed to the higher proportion of Hg partitioned to the MTLPs. Moreover, significant enhancement of Hg tolerance also was found in the F, offspring originating from the F0 mothers exposed to 25 nM of Hg, but there was no significant induction of MTLPs in these F, offspring when compared to the offspring from the control mothers. The Hg tissue concentrations in the F-1 neonates were approximately 25\% of those in the F0 adults. However, there was similar Hg tolerance in the F-2 offspring originating from both the control and Hg-exposed F-0 mothers, indicating that the Hg tolerance in the daphnids disappeared two generations after Hg contamination. Further exposure of the F, offspring to different Hg concentrations (1.5 and 15 nM for 28 d) indicated that maternal exposure history did not affect their growth and reproductive performance, which solely were influenced by the offspring exposure. Unexpectedly, the F-1 offspring exposed to Hg had significantly higher final wet weights and reproductive rates than the control groups, suggesting the possibility of Hg hormesis. Furthermore, the maternal exposure had no effect on the Hg accumulation and the MTLP concentrations in the F-1 offspring. Therefore, we concluded that the Hg tolerance might disappear quickly once the Hg contamination was removed and the maternal exposure history was not important in determining the physiological performance and Hg accumulation of the subsequent generations

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

This study examined the toxicological interaction between glyphosate (or its formulation, Roundup((R))) and several heavy metals to a freshwater cladoceran, Ceriodaphnia dubia. We demonstrated that all binary combinations of Roundup((R)) 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. (c) 2005 Elsevier Ltd. All rights reserved