PFASs-restriction proposal commentary on ECHA's Annex XV restriction report, proposal for a restriction, March 2023.

PFASs are defined as substances that contain at least one fully fluorinated methyl (CF3-) or methylene (-CF2-) carbon atom. The excellent technical properties of members of the PFAS group have led to their use in a wide range of applications. The substance group comprises more than 10,000 individual compounds. A variety of adverse effects has been described for single substances. For the majority of the PFASs, neither toxicokinetic data nor effect data is available. Hence, because of the small number of PFASs for which a full toxicological profile is available, grouping based on the existing data is not feasible. A critical problem of PFASs and their degradation products is the very high persistence, which clearly fulfils the criterion for the substance property Very Persistent (vP) according to Annex XIII of the REACH Regulation. Because of this property the European Commission is planning to take action. Defining suitable subgroups appears to be a scientifically based approach. However, to reach this goal, large data gaps would have to be closed which would take up to centuries, a time-frame, which is not defendable with respect to potential irreversible harm. Because of the time pressure resulting from the potential irreversible harm, the precautionary principle has been selected as an appropriate tool to handle PFASs and in the restriction proposal PFASs are treated as one group. This approach is justified in the view of the advisory committee of the German Society for Toxicology. ECHA's proposal received a lot of attention in the public. However, communication so far has obviously led to the misunderstanding of a proven health hazard for all PFASs. Communication should explain the justification of the broad inclusion of substances as being based on the precautionary principle. Data gaps versus current knowledge need to be clearly communicated; communication should also include the possibility for derogation of essential use. It should address the issue of suitable substitutes to avoid unintended health consequences; and it should mention that existing persistent environmental contamination calls for developing innovation in remediation techniques.

Long-term simulation of lead concentrations in agricultural soils in relation to human adverse health effects.

Lead (Pb) exposure of consumers and the environment has been reduced over the past decades. Despite all measures taken, immission of Pb onto agricultural soils still occurs, with fertilizer application, lead shot from hunting activities, and Pb from air deposition representing major sources. Little is known about the intermediate and long-term consequences of these emissions. To gain more insight, we established a mathematical model that considers input from fertilizer, ammunition, deposition from air, uptake of Pb by crops, and wash-out to simulate the resulting Pb concentrations in soil over extended periods. In a further step, human oral exposure by crop-based food was simulated and blood concentrations were derived to estimate the margin of exposure to Pb-induced toxic effects. Simulating current farming scenarios, a new equilibrium concentration of Pb in soil would be established after several centuries. Developmental neurotoxicity represents the most critical toxicological effect of Pb for humans. According to our model, a Pb concentration of ~ 5 mg/kg in agricultural soil leads to an intake of approximately 10 µg Pb per person per day by the consumption of agricultural products, the dose corresponding to the tolerable daily intake (TDI). Therefore, 5 mg Pb/kg represents a critical concentration in soil that should not be exceeded. Starting with a soil concentration of 0.1 mg/kg, the current control level for crop fields, our simulation predicts periods of ~ 50 and ~ 175 years for two Pb immission scenarios for mass of Pb per area and year [scenario 1: ~ 400 g Pb/(ha × a); scenario 2: ~ 175 g Pb/(ha × a)], until the critical concentration of ~ 5 mg/kg Pb in soil would be reached. The two scenarios, which differ in their Pb input via fertilizer, represent relatively high but not unrealistic Pb immissions. From these scenarios, we calculated that the annual deposition of Pb onto soil should remain below ~ 100 g/(ha × a) in order not to exceed the critical soil level of 5 mg/kg. We propose as efficient measures to reduce Pb input into agricultural soil to lower the Pb content of compost and to use alternatives to Pb ammunition for hunting.

Internal threshold of toxicological concern values: enabling route-to-route extrapolation.

The TTC concept uses toxicological data from animal testing to derive generic human exposure threshold values (TTC values), below which the risk of adverse effects on human health is considered to be low. It uses distributions of no-observed-adverse-effect levels (NOAELs) for substances. The 5th percentile value is divided by an uncertainty factor (100) to give a TTC value. As the toxicological data underpinning the TTC concept are from tests with oral exposure, the exposure is to be understood as an external oral exposure. For risk assessment of substances with a low absorption (by the oral route, or through skin), the internal exposure is more relevant than the external exposure. European legislation allows that tests might not be necessary for substances with negligible absorption with low internal exposure. The aim of this work is to derive internal TTC values to allow the TTC concept to be applied to situations of low internal exposure. The external NOAEL of each chemical of three databases (Munro, ELINCS, Food Contact Materials) was multiplied by the bioavailability of the individual chemical. Oral bioavailability was predicted using an in silico prediction tool (ACD Percepta). After applying a reduced uncertainty factor of 25, we derived internal TTC values. For Cramer class I, the internal TTC values are 6.9 µg/kg bw/d (90 % confidence interval: 3.8-11.5 mg/kg bw/d); for Cramer class II/III 0.1 µg/kg bw/d (90 % confidence interval: 0.08-0.14 µg/kg bw/d).

Functional UDP-glucuronyltransferase 2B15 polymorphism and bisphenol A concentrations in blood: results from physiologically based kinetic modelling.

Bisphenol A (BPA) is a chemical in widespread use that is under scientific discussion due to its endocrine activity. Controversies exist about how to interpret reportedly high blood concentrations measured in uncontrolled situations. Physiologically based pharmaco-/toxicokinetic modelling resulted in 10-100-fold lower blood concentrations than those reported. Moreover, in controlled situations, BPA did not exceed the level of detection (<0.3 ng/ml) in human blood or urine. Using a validated human PBK model, this study investigated the influence of functionally relevant polymorphic UGT2B15, the enzyme mediating BPA metabolism, on the BPA concentration-time profile in human blood. Maximum concentrations (C(max)) and areas under the curves (AUCs) in blood from high and low metabolisers differed by a factor of 4.7 and 4.6, respectively (doses: 1 and 0.05 µg/kg/day). Low metabolisers excreted a greater proportion of BPA via the sulphate pathway compared to high metabolisers. This finding explains why C(max) and AUC increased to a smaller extent, as predicted from in vitro data obtained with transfected cells possessing only the UGT2B15 variants. The highest C(max) value calculated in the subject with the lowest metabolic clearance was roughly 40 pg/ml, which is far lower than reported high blood concentrations, which in turn cannot be explained by genetically impaired UGT2B15 activity. From the risk assessment perspective, our results indicate that the traditional uncertainty factor is sufficient to account for the variability in the polymorphic glucuronidation of BPA.

Testing the thresholds of toxicological concern values using a new database for food-related substances.

The Threshold of Toxicological Concern (TTC) concept integrates data on exposure, chemical structure, toxicity and metabolism to identify a safe exposure threshold value for chemicals with insufficient toxicity data for risk assessment. The TTC values were originally derived from a non-cancer dataset of 613 compounds with a potentially small domain of applicability. There is interest to test whether the TTC values are applicable to a broader range of substances, particularly relevant to food safety using EFSA's new OpenFoodTox database. After exclusion of genotoxic compounds, organophosphates or carbamates or those belonging to the TTC exclusion categories, the remaining 329 substances in the EFSA OpenFoodTox database were categorized under the Cramer decision tree, into low (Class I), moderate (II), or high (III) toxicity profile. For Cramer Classes I and III the threshold values were 1000 µg/person per day (90% confidence interval: 187-2190) and 87 µg/person per day (90% confidence interval: 60-153), respectively, compared to the corresponding original threshold values of 1800 and 90 µg/person per day. This confirms the applicability of the TTC values to substances relevant to food safety. Cramer Class II was excluded from our analysis because of containing too few compounds. Comparison with the Globally Harmonized System of classification confirmed that the Cramer classification scheme in the TTC approach is conservative for substances relevant to food safety.

Exposure of Nursed Infants to Maternal Treatment with Ethambutol and Rifampicin.

Mycobacterial diseases remain a significant cause of morbidity and mortality worldwide. Rifampicin and ethambutol are among the drugs recommended by WHO as first-line treatment. In this work, we addressed the question whether doses of the two anti-tuberculosis agents ethambutol and rifampicin transferred to a nursed infant could be of health concerns when the mother is under treatment. We used the approach of pharmacokinetic modelling using a structural model with two interconnected organisms: the first one being the organism of the nursing mother and the second one being the organism of the nursed child. Physiological data were taken from the literature. The models were parameterised by data from the literature concerning clearance, absorption and plasma/milk ratio. Distribution into the tissues was calculated by an algorithm. The predictive power of the model was tested by comparing the predicted plasma concentrations in the mothers with measured data from the literature. Comparison with measured data after direct infant treatment was performed for the rifampicin plasma concentrations predicted in the nursed infant. Both comparisons confirmed the appropriateness of the modelling results. The transfer of 0.08 mg/kg bw/day ethambutol via breast milk to the nursed infant, the dose we have estimated, when the mother received a therapeutic dose of 24.5 mg/kg bw, can be judged as being without health concern. Likewise, for rifampicin, the transferred dose of 0.4 mg/kg bw to the nursed infant resulting from a therapeutic dose of 10.9 mg/kg bw to the mother does not raise health concerns.

Innovative Strategies to Develop Chemical Categories Using a Combination of Structural and Toxicological Properties.

Interest is increasing in the development of non-animal methods for toxicological evaluations. These methods are however, particularly challenging for complex toxicological endpoints such as repeated dose toxicity. European Legislation, e.g., the European Union's Cosmetic Directive and REACH, demands the use of alternative methods. Frameworks, such as the Read-across Assessment Framework or the Adverse Outcome Pathway Knowledge Base, support the development of these methods. The aim of the project presented in this publication was to develop substance categories for a read-across with complex endpoints of toxicity based on existing databases. The basic conceptual approach was to combine structural similarity with shared mechanisms of action. Substances with similar chemical structure and toxicological profile form candidate categories suitable for read-across. We combined two databases on repeated dose toxicity, RepDose database, and ELINCS database to form a common database for the identification of categories. The resulting database contained physicochemical, structural, and toxicological data, which were refined and curated for cluster analyses. We applied the Predictive Clustering Tree (PCT) approach for clustering chemicals based on structural and on toxicological information to detect groups of chemicals with similar toxic profiles and pathways/mechanisms of toxicity. As many of the experimental toxicity values were not available, this data was imputed by predicting them with a multi-label classification method, prior to clustering. The clustering results were evaluated by assessing chemical and toxicological similarities with the aim of identifying clusters with a concordance between structural information and toxicity profiles/mechanisms. From these chosen clusters, seven were selected for a quantitative read-across, based on a small ratio of NOAEL of the members with the highest and the lowest NOAEL in the cluster (< 5). We discuss the limitations of the approach. Based on this analysis we propose improvements for a follow-up approach, such as incorporation of metabolic information and more detailed mechanistic information. The software enables the user to allocate a substance in a cluster and to use this information for a possible read- across. The clustering tool is provided as a free web service, accessible at http://mlc-reach.informatik.uni-mainz.de.