Identifying Chemical Groups for Biomonitoring

Optimizing Chemicals Management in the United States and Canada through the Essential-Use Approach

Chemicals have improved the functionality and convenience of industrial and consumer products, but sometimes at the expense of human or ecological health. Existing regulatory systems have proven to be inadequate for assessing and managing the tens of thousands of chemicals in commerce. A different approach is urgently needed to minimize ongoing production, use, and exposures to hazardous chemicals. The premise of the essential-use approach is that chemicals of concern should be used only in cases in which their function in specific products is necessary for health, safety, or the functioning of society and when feasible alternatives are unavailable. To optimize the essential-use approach for broader implementation in the United States and Canada, we recommend that governments and businesses (1) identify chemicals of concern for essentiality assessments based on a broad range of hazard traits, going beyond toxicity; (2) expedite decision-making by avoiding unnecessary assessments and strategically asking up to three questions to determine whether the use of the chemical in the product is essential; (3) apply the essential-use approach as early as possible in the process of developing and assessing chemicals; and (4) engage diverse experts in identifying chemical uses and functions, assessing alternatives, and making essentiality determinations and share such information broadly. If optimized and expanded into regulatory systems in the United States and Canada, other policymaking bodies, and businesses, the essential-use approach can improve chemicals management and shift the market toward safer chemistries that benefit human and ecological health.

Biotransformation of bisphenol-A bis(diphenyl phosphate): In vitro, in silico, and (non-) target analysis for metabolites in rat and bird liver microsomal models

Increased production and usage of organophosphate esters (OPEs) as flame retardants and plasticizers has trended towards larger and 'novel' (oligomeric) OPEs, although there is a dearth of understanding of the environmental fate, stability, toxicokinetics, biotransformation and bioaccumulation of novel OPEs in exposed biota. The present study characterized in vitro biotransformation of the novel OPE bisphenol-A bis(diphenyl phosphate) (BPADP) using Wistar-Han rat and herring gull liver based microsomal assays. Hypothesized target metabolites bisphenol-A (BPA) and diphenyl phosphate (DPHP) and other metabolites were investigated by applying a lines of evidence approach. In silico modelling predicted both BPA and DPHP as rat metabolites of BPADP, these metabolites were quantified via UHPLC-QQQ-MS/MS. Additional non-target metabolites were determined by UHPLC-Q-Exactive-Orbitrap-HRMS/MS and identified by Compound Discoverer software. Mean BPADP depletion of 44 ± 10% was quantified with 3.9% and 2.6% conversion to BPA and DPHP, respectively, in the rat assay. BPADP metabolism was much slower when compared to the well-studied OPE, triphenyl phosphate (TPHP). BPADP depletion in gull liver assays was far slower relative to the rat. Additional non-target metabolites identified included two Phase I, O-dealkylation products, five Phase I oxidation products and one Phase II glutathione adduct, demonstrating agreement between lines of in vitro and in silico evidence. Lines of evidence suggest that BPADP is biologically persistent in exposed mammals or birds. These findings add to the understanding of BPADP stability and biotransformation, and perhaps of other novel OPEs, which are factors highly applicable to hazard assessments of exposure, persistence and bioaccumulation in biota.

Validated single urinary assay designed for exposomic multi-class biomarkers of common environmental exposures

Epidemiological studies often call for analytical methods that use a small biospecimen volume to quantify trace level exposures to environmental chemical mixtures. Currently, as many as 150 polar metabolites of environmental chemicals have been found in urine. Therefore, we developed a multi-class method for quantitation of biomarkers in urine. A single sample preparation followed by three LC injections was optimized in a proof-of-approach for a multi-class method. The assay was validated to quantify 50 biomarkers of exposure in urine, belonging to 7 chemical classes and 16 sub-classes. The classes represent metabolites of 12 personal care and consumer product chemicals (PCPs), 5 polycyclic aromatic hydrocarbons (PAHs), 5 organophosphate flame retardants (OPFRs), 18 pesticides, 5 volatile organic compounds (VOCs), 4 tobacco alkaloids, and 1 drug of abuse. Human urine (0.2 mL) was spiked with isotope-labeled internal standards, enzymatically deconjugated, extracted by solid-phase extraction, and analyzed using high-performance liquid chromatography-tandem mass spectrometry. The methanol eluate from the cleanup was split in half and the first half analyzed for PCPs, PAH, and OPFR on a Betasil C18 column; and pesticides and VOC on a Hypersil Gold AQ column. The second half was analyzed for tobacco smoke metabolites and a drug of abuse on a Synergi Polar RP column. Limits of detection ranged from 0.01 to 1.0 ng/mL of urine, with the majority ≤0.5 ng/mL (42/50). Analytical precision, estimated as relative standard deviation of intra- and inter-batch uncertainty, variabilities, was <20%. Extraction recoveries ranged from 83 to 109%. Results from the optimized multi-class method were qualified in formal international proficiency testing programs. Further method customization options were explored and method expansion was demonstrated by inclusion of up to 101 analytes of endo- and exogenous chemicals. This exposome-scale assay is being used for population studies with savings of assay costs and biospecimens, providing both quantitative results and the discovery of unexpected exposures.

BHPF exposure impairs mouse and human decidualization

Although BHPF has been widely used in plastic manufacturing as a substitute for BPA, current evidence suggests that BHPF also causes harmful effects on reproduction. However, effects of BHPF on mammalian early pregnancy are still poorly defined. This study aimed to explore the effects of BHPF on early pregnancy, especially decidualization and embryonic development in mice and human beings. The results showed that 50 and 100 mg/kg BHPF exposure reduced birth weight, and implantation site weight on the day 8 of pregnancy in mice. Because BHPF inhibits both embryo development and artificial decidualization in mice, suggesting that the detrimental effects of BHPF should be from its effects on embryo development and decidualization. Under in vitro decidualization, 10 μM BHPF inhibits decidualization and leads to disordered expression of Lamin B1 and collagen in mice. In addition, 10 μM BHPF also inhibits decidualization, and causes disordered expression of both collagen III and Lamin B1 under human in vitro decidualization. However, collagen III supplementation can rescue BHPF inhibition on decidualization. Further, our study demonstrates that BHPF impairs human decidualization through the HB-EGF/EGFR/STAT3/Collagen III pathway. Taken together these data suggest that exposure to BHPF impairs mouse and human decidualization during early pregnancy.

The Next Generation Blueprint of Computational Toxicology at the U.S. Environmental Protection Agency

The U.S. Environmental Protection Agency (EPA) is faced with the challenge of efficiently and credibly evaluating chemical safety often with limited or no available toxicity data. The expanding number of chemicals found in commerce and the environment, coupled with time and resource requirements for traditional toxicity testing and exposure characterization, continue to underscore the need for new approaches. In 2005, EPA charted a new course to address this challenge by embracing computational toxicology (CompTox) and investing in the technologies and capabilities to push the field forward. The return on this investment has been demonstrated through results and applications across a range of human and environmental health problems, as well as initial application to regulatory decision-making within programs such as the EPA's Endocrine Disruptor Screening Program. The CompTox initiative at EPA is more than a decade old. This manuscript presents a blueprint to guide the strategic and operational direction over the next 5 years. The primary goal is to obtain broader acceptance of the CompTox approaches for application to higher tier regulatory decisions, such as chemical assessments. To achieve this goal, the blueprint expands and refines the use of high-throughput and computational modeling approaches to transform the components in chemical risk assessment, while systematically addressing key challenges that have hindered progress. In addition, the blueprint outlines additional investments in cross-cutting efforts to characterize uncertainty and variability, develop software and information technology tools, provide outreach and training, and establish scientific confidence for application to different public health and environmental regulatory decisions.

The California Safer Consumer Products Program: Evaluating a Novel Chemical Policy Strategy

In 2008, California enacted laws to restructure chemical policy and promote green chemistry. Ten years after the passage of California’s green chemistry laws, we assessed their performance through structured interviews with a sample of experts from government, academia, business, and the nonprofit sector. We combined the interviews with a scoping literature review to propose a new ten-point framework for evaluating the effectiveness of a chemical regulatory policy, and we assessed the performance of the California law against this framework. The California program performed well on transparency of the regulatory process; protecting vulnerable populations; placing the primary burden on the manufacturer; breadth of regulatory authority; and advancing the public right-to-know. Areas of weakness include unclear authority to require data on chemical use in products; an inefficient pace of implementation; and limited incentives for innovation. Promoting safer chemicals in products will require additional incentives to protect public health and the environment.

Mass spectrometric identification of in vitro-generated metabolites of two emerging organophosphate flame retardants: V6 and BDP

The aim of the present study was to investigate the in vitro metabolism of two emerging organophosphate flame retardants, namely tetrekis(2-chlorethyl)dichloroisopentyldiphosphate (V6) and bisphenol-A bis-diphenyl phosphate (BDP) in human liver microsomes (HLMs), HLM S9 fractions and in human serum. In particular, the role of cytochrome P450 (CYPs) enzymes and/or paraoxonases (PONs) in the formation of V6 and BDP phase I metabolites was studied. Mono-, di-hydroxylated and hydrolytic phase I metabolites of V6 were mainly formed by CYPs in HLMs, while hydrolytic and O-dealkylated phase I metabolites of BDP were generated by PONs mainly in serum experiments. Limited number of glucuronidated and sulfated phase II metabolites were also identified for the two chemicals. The activity of seven recombinant CYPs (rCYPs) including rCYP1A2, rCYP2B6, rCYP2C9, rCYP2C19, rCYP2D6, rCYP2E1 and rCYP3A4 in the in vitro phase I metabolism of V6 and BDP was investigated. The formation of V6 metabolites was catalyzed by several enzymes, especially rCYP1A2 that was responsible for the exclusive formation of two metabolites, one primary (M1) and its secondary metabolite (M9). For BDP, only one phase I metabolite (MM1) was catalyzed by the seven rCYPs. Collectively, these results indicate that CYPs have a predominant role in the metabolism of V6, while PONs have a predominant role in BDP in vitro metabolism. These results are a starting point for future studies involving the study of the toxicity, bioaccumulation and in vivo biomonitoring of V6 and BDP.