Reproducibility of methods required to identify and characterize nanoforms of substances

Nanoforms (NFs) of a substance may be distinguished from one another through differences in their physicochemical properties. When registering nanoforms of a substance for assessment under the EU REACH framework, five basic descriptors are required for their identification: composition, surface chemistry, size, specific surface area and shape. To make the risk assessment of similar NFs efficient, a number of grouping frameworks have been proposed, which often require assessment of similarity on individual physicochemical properties as part of the group justification. Similarity assessment requires an understanding of the achievable accuracy of the available methods. It must be demonstrated that measured differences between NFs are greater than the achievable accuracy of the method, to have confidence that the measured differences are indeed real. To estimate the achievable accuracy of a method, we assess the reproducibility of six analytical techniques routinely used to measure these five basic descriptors of nanoforms: inductively coupled plasma mass spectrometry (ICP-MS), Thermogravimetric analysis (TGA), Electrophoretic light scattering (ELS), Brunauer-Emmett-Teller (BET) specific surface area and transmission and scanning electron microscopy (TEM and SEM). Assessment was performed on representative test materials to evaluate the reproducibility of methods on single NFs of substances. The achievable accuracy was defined as the relative standard deviation of reproducibility (RSD_R) for each method. Well established methods such as ICP-MS quantification of metal impurities, BET measurements of specific surface area, TEM and SEM for size and shape and ELS for surface potential and isoelectric point, all performed well, with low RSD_R, generally between 5 and 20%, with maximal fold differences usually <1.5 fold between laboratories. Applications of technologies such as TGA for measuring water content and putative organic impurities, additives or surface treatments (through loss on ignition), which have a lower technology readiness level, demonstrated poorer reproducibility, but still within 5-fold differences. The expected achievable accuracy of ICP-MS may be estimated for untested analytes using established relationships between concentration and reproducibility, but this is not yet the case for TGA measurements of loss on ignition or water content. The results here demonstrate an approach to estimate the achievable accuracy of a method that should be employed when interpreting differences between NFs on individual physicochemical properties.

Assessing the similarity of nanoforms based on the biodegradation of organic surface treatment chemicals

A substance may have one or more nanoforms, defined for regulatory purposes under EU chemicals legislation REACH based on differences in physicochemical properties such as size, shape, specific surface area and surface chemistry including coatings. To reduce the burden of testing each unique nanoform for the environmental risk assessment of nanomaterials, grouping approaches allow simultaneous assessment of multiple nanoforms. Nanoforms with initially different intrinsic properties, could still be considered similar if their environmental fate and effects can be demonstrated to be similar. One hypothesis to group nanoforms with different organic surface modifications is to use parameters linked to biodegradation of the organic surface. The hypothesis contends that nanoforms with a similar core chemistry, but different organic surface treatments may be grouped, if the surface treatment is likely to be lost through biodegradation rapidly upon entering an environmental compartment, such that it no longer modulates fate, exposure and toxicity of the nanoform. To implement grouping according to surface treatment biodegradability, a robust approach to measure the breakdown of particle surface treatments is needed. We present a tiered testing strategy to assess the biodegradation of organic surface treatments used with nanomaterials that can be implemented as part of an Integrated Approach to Testing and Assessment (IATA) for grouping based on surface treatment stability. The tiered approach consists of an initial pre-screening MT2 colorimetric carbon substrate utilisation assay, to provide a rapid assessment of coating degradation, and a second tier of testing using OECD Test Guideline 301F for assessing organic chemical biodegradability. Six common surface treatment substances are assessed using the tiered testing strategy to refine rules for escalating between tiers. Similarity assessment using absolute Euclidean distances and x-fold difference concluded that the Tier 1 assessment can be used as conservative binary screening for biodegradability (no false positive results in Tier 1), whilst for substances showing intermediate biodegradation (10-60% in OECD 301F, Tier 2), similarity assessments can be informative for grouping surface treatments not considered readily biodegradable. Further validation using higher tier tests (e.g., mesocosms) is needed to define acceptable limits of similarity between intermediately biodegradable substances, where differences in biodegradability of the surface coating lead to negligible differences in fate, behaviour and toxicity of the nanoforms, and this is critically discussed.

Comparison and evaluation of pesticide monitoring programs using a process-based mixture model

A number of European countries run large-scale pesticide monitoring schemes in watersheds aimed at identifying and evaluating the presence of pesticide residues in the environment. These schemes provide national and regional scale assessments of pesticide concentrations within the context of environmental quality assessment, aiming to ensure some degree of ecological protection. The present study is aimed at evaluating the joint effects of the pesticide mixtures detected in monitoring programs, using a process-based mixture model that was parameterized for Daphnia magna. In total, over 15 000 samples containing over 1 million individual measurements were evaluated for effects. It was found that there are only a small number of places where one can expect to have effects on daphnids, based on measured concentrations. The most polluted samples would cause extinction of a daphnid population within only 30 h. The results show that effects are mostly triggered by a limited number of pesticide residues at locations with high emissions. It was also shown that the analytical detection limits are basically too high to exclude mixture effects. So, despite all the effort that is put into chemical monitoring programs, it remains a challenge to make statements on whether or not the environment is protected. Recommendations are offered for a different setup of monitoring programs to improve this situation. Environ Toxicol Chem 2016;35:3113-3123. © 2016 SETAC.

A simple mechanistic model to interpret the effects of narcotics

In this research we will show the advantages of using a time-independent dose metric in a mechanistic model to evaluate toxic effects for different narcotic compounds on different species. We will show how different already existing QSARs can be combined within a mechanistic framework to 1) make predictions of lethal thresholds; 2) show some limitations in the use of existing QSARs; 3) show how a mechanistic framework solves some conceptual problems in current approaches and 4) show how such a framework can be used to be of aid in an experimental setup in predicting the outcome of a survival experiment. The approach we chose is based on the simplest mechanistic model available, a scaled one-compartment model to describe uptake and elimination and hazard model to link the exposure to effects on survival. Within this theoretical framework a prediction for an internal threshold for effects on survival of 3 mmol/kg bw can be made, which should be similar for different species and independent of the partitioning characteristics of the toxicant. To demonstrate this, a threshold for 51 different species was derived, which indeed appeared to lie in a relatively small range, typically between 1 and 10 mmol/kg bw.

Elimination kinetic model for organic chemicals in earthworms

Mechanistic understanding of bioaccumulation in different organisms and environments should take into account the influence of organism and chemical depending factors on the uptake and elimination kinetics of chemicals. Lipophilicity, metabolism, sorption (bioavailability) and biodegradation of chemicals are among the important factors that may significantly affect the bioaccumulation process in soil organisms. This study attempts to model elimination kinetics of organic chemicals in earthworms by accounting for the effects of both chemical and biological properties, including metabolism. The modeling approach that has been developed is based on the concept for simulating metabolism used in the BCF base-line model developed for predicting bioaccumulation in fish. Metabolism was explicitly accounted for by making use of the TIMES engine for simulation of metabolism and a set of principal transformations. Kinetic characteristics of transformations were estimated on the basis of observed kinetics data for the elimination of organic chemicals from earthworms.

Critical Limits for Hg(II) in soils, derived from chronic toxicity data

Published chronic toxicity data for Hg(II) added to soils were assembled and evaluated to produce a data set comprising 52 chronic end-points, five each for plants and invertebrates and 42 for microbes. With end-points expressed in terms of added soil Hg(II) contents, Critical Limits were derived from the 5th percentiles of species sensitivity distributions, values of 0.13 microg(g soil)(-1) and 3.3 microg(g soil organic matter)(-1) being obtained. The latter value exceeds the currently recommended Critical Limit, used to determine Hg(II) Critical Loads in Europe, of 0.5 microg(g soil organic matter)(-1). We also applied the WHAM/Model VI chemical speciation model to estimate concentrations of Hg(2+) in soil solution, and derived an approximate Critical Limit Function (CLF) that includes pH; log [Hg(2+)](crit)=-2.15 pH -17.10. Because they take soil properties into account, the soil organic matter-based limit and the CLF provide the best assessment of toxic threat for different soils. For differing representative soils, each predicts a range of up to 100-fold in the dry weight-based content of mercury that corresponds to the Critical Limit.

A hexamerin protein, AgSP-1, is associated with diapause in the boll weevil(1)

The objective of this research was to identify a reliable biochemical indicator for diapause (dormancy) in the boll weevil, Anthonomus grandis. Hemolymph polypeptides from reproductive and diapausing weevils were compared using denaturing sodium dodecyl sulpfate (SDS)-polyacrylamide gel electrophoresis (PAGE). A 77-kDa protein, which proved to be a hexamerin (AgSP-1), strongly correlated with morphological diapause characters in both male and female adult weevils. N-terminal sequence analysis identified the first 25 amino acids of the mature protein and was used to develop an antibody to AgSP-1. Anti-AgSP-1 reacted only with hemolymph from diapausing weevils of both sexes but not with hemolymph from reproductive weevils. Also, the yolk protein, vitellogenin (VG), inversely correlated with AgSP-1. When hemolymph VG was high, AgSP-1 was absent or barely perceptible.Juvenile hormone regulates VG synthesis in most insect species. Juvenile hormone is reported to stimulate reproductive maturation in the boll weevil (Physiological Entomology 22 (1997) 261) and to be absent during diapause (Physiological Entomology 22 (1997a) 269). Therefore, the juvenile hormone (JH) mimic, methoprene, was used to assess the role of JH activity in the boll weevil for terminating diapause, stimulating reproductive maturation and possibly influencing AgSP-1 titers. Application of methoprene was not effective in activating reproductive development. Hemolymph from methoprene-treated, females contained VG and AgSP-1 titers that were similar to acetone-treated and untreated control weevils.Using a genomic DNA library and 3' RACE, two clones were isolated that yielded the complete sequence of AgSP-1 as well as a portion of the 5' untranslated region. Northern blot analysis confirmed the presence of a 2.5 kB transcript for AgSP-1 in the fat body of diapausing weevils. AgSP-1 was also present in the fat body of reproductive weevils, but to a lesser extent. No sex-related differences in gene expression were observed; diapausing weevils of both sexes showed similar levels of AgSP-1 expression. An inverse correlation was observed between the VG transcript and AgSP-1 mRNA. VG was highly expressed in the fat body of reproductive females and only slightly expressed in tissue from diapausing females. Our data suggests that AgSP-1 is a diapause-specific protein in adult weevils and that JH, alone, is not effective in terminating diapause.