Dermal measurement of exposure to plant protection products: Actual hand exposure from hand washing vs. wearing cotton gloves.

For the authorization of plant protection products, a quantitative non-dietary exposure risk assessment relies on established dermal exposure models, measured mainly using passive dosimetry. Exposure to the hands is determined via hand washing or using cotton gloves as a surrogate for skin. This study compared both methods using operator exposure data available from the Agricultural Operator Exposure Model (AOEM) project report. These data indicate that hand exposure determined using cotton gloves resulted in markedly higher exposure values for all exposure scenarios compared to those determined by hand washes. One explanation for this is that dermal uptake of the residues reduces the amount of residue that can be recovered by hand washing. Uncertainty due to dermal uptake can be addressed by either default assumptions or by specific dermal absorption data. However, this cannot solely account for the large difference observed between the values and is mainly likely to be due to the higher capacity of the cotton gloves vs. human skin to retain residues. The results further indicate that the variability between hand wash samples and cotton glove samples differs between the exposure scenarios. Hence, the level of conservatism related to the use of cotton gloves as surrogate skin remains unknown. In conclusion, this evaluation of the AOEM data indicates that the cotton glove method results in much higher levels of measured hand exposure than the hand wash method. It cannot be excluded that dermal uptake has contributed to that result. However, the findings suggest the higher retention capacity of cotton gloves vs. human skin to be the main impact parameter. The cotton glove method does not provide the results with regards to the protection level that can be expected from the use of protective gloves. Therefore, we believe that the application of the hand wash method is a more accurate measure of exposure levels, if either specific dermal absorption data or, in its absence, default assumptions are applied as adjustment factor.

Dose Setting for Dermal Absorption Studies on Dried Foliar Residues.

Currently, the standard approach to estimate systemic exposure of workers after contact with dried pesticide residues on crops during re-entry activities relies on using the highest identified dermal absorption value for aqueous spray dilutions. However, recent dermal absorption studies with dried residues and their respective in-use dilutions have shown that this is likely to significantly overestimate their dermal penetration potential and, thus, predicted systemic exposure. The choice of appropriate dose levels for these dermal absorption studies has not been defined. Moreover, actual skin loading during re-entry tasks may differ significantly from that achieved by applying a fixed volume of an aqueous dilution, which is the standard practice in generic dermal absorption studies. To address this, we propose an approach to dose setting for dried residue studies within the current European risk assessment framework. Skin loading for studies can be calculated from the existing exposure algorithms and by taking appropriate body surface areas into account. Thus, skin loading in studies will vary depending on the exact nature and duration of the task and the region of the body exposed, reflecting actual exposure scenarios.

Compounded conservatism in European re-entry worker risk assessment of pesticides.

We review the risk parameters and drivers in the current European Union (EU) worker risk assessment for pesticides, for example considering crop maintenance, crop inspection or harvesting activities, and show that the current approach is very conservative due to multiple worst-case default assumptions. As a case study, we compare generic exposure model estimates with measured worker re-entry exposure values which shows that external cumulative exposure is overpredicted by about 50-fold on average. For this exercise, data from 16 good laboratory practice (GLP)-compliant worker exposure studies in 6 crops were evaluated with a total number of 184 workers. As generic overprediction does not allow efficient risk management or realistic risk communication, we investigate how external exposure can be better predicted within the generic model, and outline options for possible improvements in the current methodology. We show that simply using averages achieves more meaningful exposure estimates, while still being conservative, with an average exposure overprediction of about 9-fold. Overall, EU risk assessment includes several numerically unaccounted "hidden safety factors", which means that workers are well protected; but simultaneously risk assessments are biased towards failing due to compounded conservatism. This should be considered for further global or regional guidance developments and performing more exposure-relevant risk assessment.

Improvements in Modelling Bystander and Resident Exposure to Pesticide Spray Drift: Investigations into New Approaches for Characterizing the 'Collection Efficiency' of the Human Body.

The BREAM (Bystander and Resident Exposure Assessment Model) (Kennedy et al. in BREAM: A probabilistic bystander and resident exposure assessment model of spray drift from an agricultural boom sprayer. Comput Electron Agric 2012;88:63-71) for bystander and resident exposure to spray drift from boom sprayers has recently been incorporated into the European Food Safety Authority (EFSA) guidance for determining non-dietary exposures of humans to plant protection products. The component of BREAM, which relates airborne spray concentrations to bystander and resident dermal exposure, has been reviewed to identify whether it is possible to improve this and its description of variability captured in the model. Two approaches have been explored: a more rigorous statistical analysis of the empirical data and a semi-mechanistic model based on established studies combined with new data obtained in a wind tunnel. A statistical comparison between field data and model outputs was used to determine which approach gave the better prediction of exposures. The semi-mechanistic approach gave the better prediction of experimental data and resulted in a reduction in the proposed regulatory values for the 75th and 95th percentiles of the exposure distribution.

Interspecific differences between D. pulex and D. magna in tolerance to cyanobacteria with protease inhibitors.

It is known that cyanobacteria negatively affect herbivores due to their production of toxins such as protease inhibitors. In the present study we investigated potential interspecific differences between two major herbivores, Daphnia magna and Daphnia pulex, in terms of their tolerance to cyanobacteria with protease inhibitors. Seven clones each of D. magna and of D. pulex were isolated from different habitats in Europe and North America. To test for interspecific differences in the daphnids' tolerance to cyanobacteria, their somatic and population growth rates were determined for each D. magna and D. pulex clone after exposure to varying concentrations of two Microcystis aeruginosa strains. The M. aeruginosa strains NIVA and PCC(-) contained either chymotrypsin or trypsin inhibitors, but no microcystins. Mean somatic and population growth rates on a diet with 20% NIVA were significantly more reduced in D. pulex than in D. magna. On a diet with 10% PCC(-), the population growth of D. pulex was significantly more reduced than that of D. magna. This indicates that D. magna is more tolerant to cyanobacteria with protease inhibitors than D. pulex. The reduction of growth rates was possibly caused by an interference of cyanobacterial inhibitors with proteases in the gut of Daphnia, as many other conceivable factors, which might have been able to explain the reduced growth, could be excluded as causal factors. Protease assays revealed that the sensitivities of chymotrypsins and trypsins to cyanobacterial protease inhibitors did not differ between D. magna and D. pulex. However, D. magna exhibited a 2.3-fold higher specific chymotrypsin activity than D. pulex, which explains the observed higher tolerance to cyanobacterial protease inhibitors of D. magna. The present study suggests that D. magna may control the development of cyanobacterial blooms more efficiently than D. pulex due to differences in their tolerance to cyanobacteria with protease inhibitors.

Molecular mechanisms of tolerance to cyanobacterial protease inhibitors revealed by clonal differences in Daphnia magna.

Protease inhibitors of primary producers are a major food quality constraint for herbivores. In nutrient-rich freshwater ecosystems, the interaction between primary producers and herbivores is mainly represented by Daphnia and cyanobacteria. Protease inhibitors have been found in many cyanobacterial blooms. These inhibitors have been shown (both in vitro and in situ) to inhibit the most important group of digestive proteases in the daphnid's gut, that is, trypsins and chymotrypsins. In this study, we fed four different Daphnia magna genotypes with the trypsin-inhibitor-containing cyanobacterial strain Microcystis aeruginosa PCC 7806 Mut. Upon exposure to dietary trypsin inhibitors, all D. magna genotypes showed increased gene expression of digestive trypsins and chymotrypsins. Exposure to dietary trypsin inhibitors resulted in increased activity of chymotrypsins and reduced activity of trypsin. Strong intraspecific differences in tolerance of the four D. magna genotypes to the dietary trypsin inhibitors were found. The degree of tolerance depended on the D. magna genotype. The genotypes' tolerance was positively correlated with the residual trypsin activity and the different IC(50) values of the trypsins. On the genetic level, the different trypsin loci varied between the D. magna genotypes. The two tolerant Daphnia genotypes that both originate from the same lake, which frequently produces cyanobacterial blooms, clustered in a neighbour-joining phylogenetic tree based on the three trypsin loci. This suggests that the genetic variability of trypsin loci was an important cause for the observed intraspecific variability in tolerance to cyanobacterial trypsin inhibitors. Based on these findings, it is reasonable to assume that such genetic variability can also be found in natural populations and thus constitutes the basis for local adaptation of natural populations to dietary protease inhibitors.