Biomonitoring for workplace exposure to copper and its compounds is currently not interpretable.

This paper sets out to explore the requirements needed to recommend a useable and reliable biomonitoring system for occupational exposure to copper and its inorganic compounds. Whilst workplace environmental monitoring of copper is used to measure ambient air concentrations for comparison against occupational exposure limits, biological monitoring could provide complementary information about the internal dose of workers, taking into account intra-individual variability and exposure from all routes. For biomonitoring to be of reliable use for copper, a biomarker and the analytical ability to measure it with sufficient sensitivity must be identified and this is discussed in a range of matrices. In addition, there needs to be a clear understanding of the dose-response relationship of the biomarker with any health-effect (clinical or sub-clinical) or, between the level of external exposure (by any route) and the level of the copper biomarker in the biological matrix being sampled, together with a knowledge of the half-life in the body to determine accurate sampling times. For many biologically non-essential metals the requirements for reliable biomarkers can be met, however, for 'essential' metals such as copper that are under homeostatic control, the relationship between exposure (short- or long-term) and the level of any copper biomarker in the blood or urine is complex, which may limit the use and interpretation of measured levels. There are a number of types of biomarker guidance values currently in use which are discussed in this paper, but no values have yet been determined for copper (or its inorganic compounds) due to the complexity of its essential nature; the US The American Conference of Governmental Industrial Hygienists (ACGIH) has however indicated that it is considering the development of a biological exposure index for copper and its compounds. In light of this, we present a review of the reliability of current copper biomarkers and their potential use in the occupational context to evaluate whether there is value in carrying out human biomonitoring for copper exposure. Based on the available evidence we have concluded that the reliable use of biomonitoring of occupational exposure to copper and its application in risk assessment is not possible at the present time.

Comment on Balwierz et al. Potential Carcinogens in Makeup Cosmetics. Int. J. Environ. Res. Public Health 2023, 20, 4780.

We read with interest the article by Balwierz et al. [...].

Toxicokinetic study following intratracheal instillation or oral gavage of two [7Be]-tagged carbon black samples.

BACKGROUND: The toxicokinetic behaviour of nanostructured particles following pulmonary or oral deposition is of great scientific interest. In this toxicokinetic study, following the general principles of OECD TG 417, the systemic availability of carbon black, a nanostructured material consisting of agglomerated aggregates was characterised. METHODS: Each of two grades of beryllium-7 labelled carbon black (Monarch® 1000, oxidized and Printex® 90; untreated) was administered either intratracheally or orally to adult rats. Independent of route, rats received a single dose of approximately 0.3 mg radiolabelled carbon black. A total of 12 rats were treated per grade and per exposure route: 4 females each for feces/urine/organs and serial blood kinetics; 4 males for organs. At necropsy, the complete suite of organs was analysed for females, but only the lungs, liver, kidney, reproductive organs for males. RESULTS: In the pulmonarily exposed animals, 7Be-Monarch® 1000 and 7Be-Printex® 90 was detected in feces in the first 3 days after treatment at significant levels, i.e. 17.6% and 8.2%, respectively. In urine, small percentages of 6.7% and 0.4% were observed, respectively. In blood, radioactivity, representative of carbon black was within the background noise of the measurement method. At necropsy, 20 days post-instillation, both test items were practically exclusively found in lungs (75.1% and 91.0%, respectively) and in very small amounts (approximately 0.5%) in the lung-associated lymph nodes (LALN). In the other organs/tissues the test item was not detectable. BAL analyses indicated that carbon black particles were completely engulfed by alveolar macrophages. In orally exposed animals, 98% (7Be-Monarch® 1000) and 99% (7Be-Printex® 90) of the measured radioactivity was detected in feces. Excretion was complete within the first 3 days following treatment. 1.3% and 0.5% of measured activity was attributable to urine in animals that received 7Be-Monarch® 1000 and 7Be-Printex® 90, respectively. Radioactivity was absent in blood and other organs and tissues. CONCLUSION: Radioactivity, representative of carbon black, was not detected beyond the experimentally defined limit of quantitation systemically after deposition in lungs or stomach in rats. Under these experimental conditions, the two CB samples were not shown to translocate beyond the lung or the GI tract into the blood compartment.

Inhalation toxicity of copper compounds: Results of 14-day range finding study for copper sulphate pentahydrate and dicopper oxide and 28-day subacute inhalation exposure of dicopper oxide in rats.

Inhalation exposure to copper may occur during a range of occupational activities and the purpose of this study was to characterise the toxicological response to repeated inhalation of two copper compounds, representative of copper substances in large-scale production/use. Crl:CD(SD) rats were repeatedly exposed to aerosols of dicopper oxide (Cu2O) or copper sulphate pentahydrate (CuSO4.5 H2O) for 14-days as part of a range finding study at normalised copper doses of 0.18, 0.71, 1.78 and 8.9 mg/m3 Cu. Within a 28-days main study (Cu2O only), animals were repeatedly exposed to 0.2, 0.4, 0.8 and 2.0 mg/m3 Cu2O following OECD TG 412. The main study also consisted of satellite groups exposed for 1-, 2- or 3- weeks as well as a 13-week post-exposure recovery period group. Repeated exposure for 14-days to both copper compounds, normalised for copper content, led to an acute influx of polymorphonuclear leukocytes (neutrophils) and macrophages whilst only CuSO4.5 H2O exposure resulted in epithelial hyperplasia. This differential response may reflect the highly dissolvable nature of CuSO4.5 H2O in lung lining fluid leading to a release of copper ions at the epithelial surface whilst Cu2O is relatively indissolvable at neutral pH. In the 28-day study with Cu2O, an increase in cellularity was also evident in both histological and BALF samples and was dose-related with minimal to mild (neutrophilic) inflammation observed > 0.4 mg/m3 in the lung tissue sections and significant increases from 0.2 mg/m3 in BALF. There were no minimal haematological findings, no clinical findings and systemic organs were unaffected by inhalation exposure to dicopper oxide. The lung cellular response was limited to alveolar histiocytosis and neutrophil influx with no evidence of epithelial hyperplasia or fibrosis and all lung biomarkers returned to control levels within the post-exposure recovery period. Interestingly, the satellite groups showed that this acute cellular response followed a biphasic rather than monotonic pattern with a peak in lung biomarkers between weeks 1-3 and reduction thereafter. This reduction in lung biomarkers occurred during continued exposure and may indicate an adaptive response to copper exposure. Overall, these results show that repeated exposure to copper compounds results in an acute cellular response with no associated pathology and which fully resolved after the cessation of exposure. Therefore, the cellular response is evidence of a controlled and adaptive response associated with the removal of Cu2O from the alveolar surface.

Comment on Saber et al. (2019), "Commentary: the chronic inhalation study in rats for assessing lung cancer risk may be better than its reputation".

In their Commentary Saber et al. (Part Fibre Toxicol 16: 44, 2019) argue that chronic inhalation studies in rats can be used for assessing the lung cancer risk of insoluble nanomaterials. The authors make several significant errors in their interpretation and representation of the underlying science. In this Letter to the Editor we discuss these inaccuracies to correct the scientific record. When the science is recounted accurately it does not support Saber et al's statements and conclusions.

Managing Occupational Exposure to Welding Fume: New Evidence Suggests a More Precautionary Approach is Needed.

Welding is a common industrial process with many millions of workers exposed worldwide. In October 2017, the International Agency for Research on Cancer (IARC) concluded that exposure to welding fumes causes lung cancer in humans, based primarily on the available epidemiological literature. These research studies did not show that the cancer risk differed between mild steel and stainless steel welding but were related to the total welding aerosol. Lung cancer risks were observable at very low exposure levels; below 1 mg m-3 and perhaps as low as 0.1 mg m-3, averaged over a working lifetime. As a result of this IARC evaluation, in Britain, the Health and Safety Executive has acted to strengthen its enforcement expectations for fume control at welding activities. In the light of these developments, it would seem appropriate to review current health-based exposure limits for metal dust and fumes from welding to ensure they are protective.

Carbon Black and Lung Cancer Mortality-A Meta-regression Analysis Based on Three Occupational Cohort Studies.

OBJECTIVES: We review three large cohort studies of occupational exposure to carbon black and association with lung cancer mortality, and conduct a meta-regression to derive an exposure-response relationship. METHODS: Meta-regression analysis of cumulative exposure to carbon black and lung cancer mortality was conducted based on the relative risk estimates reported by three cohort studies of production workers from US, UK, and Germany. RESULTS: A 10 mg/m yr increase in cumulative exposure to carbon black was associated with a relative risk decrease of 1% (relative risk [RR] = 0.99; 95% confidence interval [CI]: 0.87-1.13) for lung cancer mortality. No exposure-response relationship was observed. CONCLUSIONS: This meta-regression analysis of three large occupational mortality studies reports that historic workplace exposures to carbon black were not associated with a significant risk of lung cancer.

Silica, silicosis and lung cancer: what level of exposure is acceptable?

Silica, silicosis and lung cancer: what level of exposure is acceptable?

Evaluating the evidence on genotoxicity and reproductive toxicity of carbon black: a critical review.

Carbon black is produced industrially by the partial combustion or thermal decomposition of gaseous or liquid hydrocarbons under controlled conditions. It is considered a poorly soluble, low toxicity (PSLT) particle. Recently, results from a number of published studies have suggested that carbon black may be directly genotoxic, and that it may also cause reproductive toxicity. Here, we review the evidence from these studies to determine whether carbon black is likely to act as a primary genotoxicant or reproductive toxicant in humans. For the genotoxicity endpoint, the available evidence clearly shows that carbon black does not directly interact with DNA. However, the study results are consistent with the mechanism that, at high enough concentrations, carbon black causes inflammation and oxidative stress in the lung leading to mutations, which is a secondary genotoxic mechanism. For the reproductive toxicity endpoint for carbon black, to date, there are various lung instillation studies and one short-term inhalation study that evaluated a selected number of reproduction endpoints (e.g. gestational and litter parameters) as well as other general endpoints (e.g. gene expression, neurofunction, DNA damage); usually at one time point or using a single dose. It is possible that some of the adverse effects observed in these studies may be the result of non-specific inflammatory effects caused by high exposure doses. An oral gavage study reported no adverse reproductive or developmental effects at the highest dose tested. The overall weight of evidence indicates that carbon black should not be considered a direct genotoxicant or reproductive toxicant.

Severity scoring of manganese health effects for categorical regression.

Characterizing the U-shaped exposure response relationship for manganese (Mn) is necessary for estimating the risk of adverse health from Mn toxicity due to excess or deficiency. Categorical regression has emerged as a powerful tool for exposure-response analysis because of its ability to synthesize relevant information across multiple studies and species into a single integrated analysis of all relevant data. This paper documents the development of a database on Mn toxicity designed to support the application of categorical regression techniques. Specifically, we describe (i) the conduct of a systematic search of the literature on Mn toxicity to gather data appropriate for dose-response assessment; (ii) the establishment of inclusion/exclusion criteria for data to be included in the categorical regression modeling database; (iii) the development of a categorical severity scoring matrix for Mn health effects to permit the inclusion of diverse health outcomes in a single categorical regression analysis using the severity score as the outcome variable; and (iv) the convening of an international expert panel to both review the severity scoring matrix and assign severity scores to health outcomes observed in studies (including case reports, epidemiological investigations, and in vivo experimental studies) selected for inclusion in the categorical regression database. Exposure information including route, concentration, duration, health endpoint(s), and characteristics of the exposed population was abstracted from included studies and stored in a computerized manganese database (MnDB), providing a comprehensive repository of exposure-response information with the ability to support categorical regression modeling of oral exposure data.

Implementing systematic review techniques in chemical risk assessment: Challenges, opportunities and recommendations.

Systematic review (SR) is a rigorous, protocol-driven approach designed to minimise error and bias when summarising the body of research evidence relevant to a specific scientific question. Taking as a comparator the use of SR in synthesising research in healthcare, we argue that SR methods could also pave the way for a "step change" in the transparency, objectivity and communication of chemical risk assessments (CRA) in Europe and elsewhere. We suggest that current controversies around the safety of certain chemicals are partly due to limitations in current CRA procedures which have contributed to ambiguity about the health risks posed by these substances. We present an overview of how SR methods can be applied to the assessment of risks from chemicals, and indicate how challenges in adapting SR methods from healthcare research to the CRA context might be overcome. Regarding the latter, we report the outcomes from a workshop exploring how to increase uptake of SR methods, attended by experts representing a wide range of fields related to chemical toxicology, risk analysis and SR. Priorities which were identified include: the conduct of CRA-focused prototype SRs; the development of a recognised standard of reporting and conduct for SRs in toxicology and CRA; and establishing a network to facilitate research, communication and training in SR methods. We see this paper as a milestone in the creation of a research climate that fosters communication between experts in CRA and SR and facilitates wider uptake of SR methods into CRA.

Translational toxicology in setting occupational exposure limits for dusts and hazard classification - a critical evaluation of a recent approach to translate dust overload findings from rats to humans.

BACKGROUND: We analyze the scientific basis and methodology used by the German MAK Commission in their recommendations for exposure limits and carcinogen classification of "granular biopersistent particles without known specific toxicity" (GBS). These recommendations are under review at the European Union level. We examine the scientific assumptions in an attempt to reproduce the results. MAK's human equivalent concentrations (HECs) are based on a particle mass and on a volumetric model in which results from rat inhalation studies are translated to derive occupational exposure limits (OELs) and a carcinogen classification. METHODS: We followed the methods as proposed by the MAK Commission and Pauluhn 2011. We also examined key assumptions in the metrics, such as surface area of the human lung, deposition fractions of inhaled dusts, human clearance rates; and risk of lung cancer among workers, presumed to have some potential for lung overload, the physiological condition in rats associated with an increase in lung cancer risk. RESULTS: The MAK recommendations on exposure limits for GBS have numerous incorrect assumptions that adversely affect the final results. The procedures to derive the respirable occupational exposure limit (OEL) could not be reproduced, a finding raising considerable scientific uncertainty about the reliability of the recommendations. Moreover, the scientific basis of using the rat model is confounded by the fact that rats and humans show different cellular responses to inhaled particles as demonstrated by bronchoalveolar lavage (BAL) studies in both species. CONCLUSION: Classifying all GBS as carcinogenic to humans based on rat inhalation studies in which lung overload leads to chronic inflammation and cancer is inappropriate. Studies of workers, who have been exposed to relevant levels of dust, have not indicated an increase in lung cancer risk. Using the methods proposed by the MAK, we were unable to reproduce the OEL for GBS recommended by the Commission, but identified substantial errors in the models. Considerable shortcomings in the use of lung surface area, clearance rates, deposition fractions; as well as using the mass and volumetric metrics as opposed to the particle surface area metric limit the scientific reliability of the proposed GBS OEL and carcinogen classification.

Inter- and intra-individual variation in urinary biomarker concentrations over a 6-day sampling period. Part 1: metals.

The aim of the current HBM-study is to further the understanding of the impact of inter- and intra-individual variability in HBM surveys as it may have implications for the design and interpretation of the study outcomes. As spot samples only provide a snapshot in time of the concentrations of chemicals in an individual, it remains unclear to what extent intra-individual variability plays a role in the overall variability of population-wide HBM surveys. The current paper describes the results of an intensive biomonitoring study, in which all individual urine samples of 8 individuals were collected over a 6-day sampling period (a total of 352 unique samples). By analyzing different metals (As, Cd, Mn, Ni) in each individual sample, inter- and intra-individual variability for these four metals could be determined, and the relationships between exposure, internal dose, and sampling protocol assessed. Although the range of biomarker values for different metals was well within the normal range reported in large-scale population surveys, large intra-individual differences over a 6-day period could also be observed. Typically, measured biomarker values span at least an order of magnitude within an individual, and more if specific exposure episodes could be identified. Fish consumption for example caused a twenty- to thirty-fold increase in urinary As-levels over a period of 2-6h. Intra-class correlation coefficients (ICC) were typically low for uncorrected biomarker values (between 0.104 and 0.460 for the 4 metals), but improved when corrected for creatinine or specific gravity (SG). The results show that even though urine is a preferred matrix for HBM studies, there are certain methodological issues that need to be taken into account in the interpretation of urinary biomarker data, related to the intrinsic variability of the urination process itself, the relationship between exposure events and biomarker quantification, and the timing of sampling. When setting up HBM-projects, this expected relationship between individual exposure episode and urinary biomarker concentration needs to be taken into account.

Inter- and intra-individual variation in urinary biomarker concentrations over a 6-day sampling period. Part 2: personal care product ingredients.

An intensive study was conducted to provide data on intra- and inter-individual variation in urinary excretion of a series of ingredients in personal care products (parabens, triclosan, benzophenones) and bisphenol A (BPA, not expected to be an ingredient) in 8 volunteers over 6 days. Exposure diaries recorded use of personal care products with identified target analytes as ingredients. Participants' usual products were replaced with products without the target analytes for 2 of the 6 days. Urine void volumes and times were recorded. Methyl, ethyl, and n-propylparabens, triclosan, benzophenone-3, and BPA were frequently detected (≥70% of samples). Urinary concentrations of the parabens and triclosan were lower on product replacement days. First morning void concentrations correlated moderately to highly with 24-h composite concentrations for all analytes. Intraclass correlation coefficients (ICCs) for spot samples collected on days with usual product use were low for BPA (0.15), moderate for n-propylparaben and methylparaben (0.39 and 0.56, respectively), and high for ethylparaben, benzophenone-3, and triclosan (0.76, 0.81, and 0.934, respectively); ICCs were consistently higher on the basis of cr-adjusted concentrations. Hydration status adjustment methods were assessed by comparing unadjusted and adjusted concentrations to urinary excretion rates (ER, ng/kg-h) for all analytes and samples. Specific gravity-adjusted concentrations correlated slightly better with ER than creatinine-adjusted concentrations. Within-individual variation in biomarker concentrations was highest for methyl and ethylparabens (2 orders of magnitude variation in spot sample concentrations) and lower for the other analytes (1-1.5 orders of magnitude). This dataset provides insight into the design and interpretation of urinary biomonitoring studies for non-persistent chemicals.

Sources of variability in biomarker concentrations.

Human biomonitoring has become a primary tool for chemical exposure characterization in a wide variety of contexts: population monitoring and characterization at a national level, assessment and description of cohort exposures, and individual exposure assessments in the context of epidemiological research into potential adverse health effects of chemical exposures. The accurate use of biomonitoring as an exposure characterization tool requires understanding of factors, apart from external exposure level, that influence variation in biomarker concentrations. This review provides an overview of factors that might influence inter- and intraindividual variation in biomarker concentrations apart from external exposure magnitude. These factors include characteristics of the specific chemical of interest, characteristics of the likely route(s) and frequency of exposure, and physiological characteristics of the biomonitoring matrix (typically, blood or urine). Intraindividual variation in biomarker concentrations may be markedly affected by the relationship between the elimination half-life and the intervals between exposure events, as well as by variation in characteristics of the biomonitored media such as blood lipid content or urinary flow rate. Variation across individuals may occur due to differences in time of sampling relative to exposure events, physiological differences influencing urinary flow or creatinine excretion rates or blood characteristics, and interindividual differences in metabolic rate or other factors influencing the absorption or excretion rate of a compound. Awareness of these factors can assist researchers in improving the design and interpretation of biomonitoring studies.