Commercial chemicals are used extensively across urban centres worldwide1, posing a potential exposure risk to 4.2 billion people2. Harmful chemicals are often assessed on the basis of their environmental persistence, accumulation in biological organisms and toxic properties, under international and national initiatives such as the Stockholm Convention3. However, existing regulatory frameworks rely largely upon knowledge of the properties of the parent chemicals, with minimal consideration given to the products of their transformation in the atmosphere. This is mainly due to a dearth of experimental data, as identifying transformation products in complex mixtures of airborne chemicals is an immense analytical challenge4. Here we develop a new framework—combining laboratory and field experiments, advanced techniques for screening suspect chemicals, and in silico modelling—to assess the risks of airborne chemicals, while accounting for atmospheric chemical reactions. By applying this framework to organophosphate flame retardants, as representative chemicals of emerging concern5, we find that their transformation products are globally distributed across 18 megacities, representing a previously unrecognized exposure risk for the world’s urban populations. More importantly, individual transformation products can be more toxic and up to an order-of-magnitude more persistent than the parent chemicals, such that the overall risks associated with the mixture of transformation products are also higher than those of the parent flame retardants. Together our results highlight the need to consider atmospheric transformations when assessing the risks of commercial chemicals.
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The RAIDAR model is implemented in a user-friendly online platform named the Exposure and Safety Estimation (EAS-E) Suite, which is free for online use at www.eas-e-suite.com.
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We thank J. A. Arnot for providing the codes for the latest version of the RAIDAR model. We acknowledge funding support from the Air Pollution programme of Environment and Climate Change Canada (ECCC). This work was also partially funded by the Chemicals Management Plan (CMP). It does not reflect any regulatory conclusions for any substances mentioned.
The authors declare no competing interests.
Peer review information Nature thanks Kevin Jones and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer review reports are available.
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Extended data figures and tables
Extended Data Fig. 1 Chemical structures of OPFR parent compounds and transformation products studied here.
a, Nine OPFR parent compounds. b, Ten OPFR transformation products identified in GAPS–MC field samples. TCEP-1 and TCPP-25 (see Supplementary Table 1) are difficult to distinguish from each other as they have identical chemical formulae. However, given that TCEP-1 and TCPP-25 are formed through one-step and two-step photooxidation reactions, respectively, and given that the oxidation timescales associated with urban regions are short23, TCEP-1 is likely to be the dominant product.
Photooxidation reactions proceed predominantly through three main channels. a, OH addition to the substituents attached to the phosphate centre (channel 1). b, OH addition to the phosphate centre (channel 2). c, Photodecomposition of early-generation products (channel 3). Generalized examples for chlorinated and non-chlorinated OPFRs are shown here. Detailed mechanisms for TCPP (a chlorinated OPFR) and EHDP (a non-chlorinated OPFR) are shown in Supplementary Figs. 1, 2.
Extended Data Fig. 3 Mass chromatograms and spectra for six OPFR transformation products in OFR laboratory samples and GAPS–MC field samples.
This information is used in the identification of: a, TCEP-1; b, TCEP-10; c, TCEP-21; d, TCPP-9; e, TCPP-21; and f, TCPP-38. Detailed product information—including chemical formulae, retention times, measured m/z values, isotopic ratios, detection frequencies and concentrations—is summarized in Supplementary Tables 2, 4.
Extended Data Fig. 4 Mass chromatograms and spectra of four OPFR transformation products in OFR laboratory samples and GAPS–MC field samples.
This information is used in the identification of: a, TDCPP-14; b, TBEP-36; c, TPhP-6; and d, TPhP-8. Detailed product information—including chemical formulae, retention times, measured m/z values, isotopic ratios, detection frequencies and concentrations—is summarized in Supplementary Tables 2, 4.
Extended Data Fig. 5 Seasonal variation in Rsignal in Toronto, Canada, as a measure of photochemical production of OPFR products.
Rsignal is the ratio of the signal intensity of an OPFR product to the signal intensity of the corresponding parent OPFR. A higher Rsignal is indicative of increased photooxidation in the summer months. Samples were collected during summer (August to September 2016) and winter (December 2016 to January 2017).
a, Modelled overall persistence for three chlorinated OPFRs (TCEP, TCPP and TDCPP) and their products. b, Modelled overall persistence for six non-chlorinated OPFRs (TBEP, TPhP, EHDP, TCP, TEHP and DPhP) and their products. c, Relative persistence for three chlorinated OPFRs and their transformation products (parent compound = 1). d, Relative persistence for six non-chlorinated OPFRs and their transformation products. Dark red, light red, dark blue and light blue represent chlorinated parent OPFRs, chlorinated OPFR products, non-chlorinated parent OPFRs, and non-chlorinated OPFR products, respectively. Note that a higher overall persistence indicates a higher persistence in the multimedia environment. Compounds marked with asterisks are those identified in megacity field samples.
Extended Data Fig. 7 Octanol–air (log KOA) and octanol–water (log KOW) partition coefficients for OPFRs and their transformation products at a pH of 7.
Dark red, light red, dark blue and light blue represent chlorinated parent OPFRs, chlorinated OPFR products, non-chlorinated parent OPFRs and non-chlorinated OPFR products, respectively.
Extended Data Fig. 8 Bioaccumulation of OPFRs and their transformation products in aquatic organisms.
a, Modelled bioconcentration factor (BCF) for three chlorinated OPFRs (TCEP, TCPP and TDCPP) and their products. b, Modelled bioconcentration factor for six non-chlorinated OPFRs (TBEP, TPhP, EHDP, TCP, TEHP and DPhP) and their products. c, Relative bioaccumulation for three chlorinated OPFRs and their transformation products (parent compound = 1). d, Relative bioaccumulation for six non-chlorinated OPFRs and their transformation products. Dark red, light red, dark blue and light blue represent chlorinated parent OPFRs, chlorinated OPFR products, non-chlorinated parent OPFRs and non-chlorinated OPFR products, respectively. Note that a higher bioconcentration factor indicates a higher potential for bioaccumulation in aquatic organisms. Compounds marked with asterisks are those identified in megacity field samples.
a, Modelled fathead minnow LC50 values for three chlorinated OPFRs (TCEP, TCPP and TDCPP) and their products. b, Modelled fathead minnow LC50 values for six non-chlorinated OPFRs (TBEP, TPhP, EHDP, TCP, TEHP and DPhP) and their products. c, Relative toxicity for three chlorinated OPFRs and their transformation products (parent compound = 1). d, Relative toxicity for six non-chlorinated OPFRs and their transformation products. Dark red, light red, dark blue and light blue represent chlorinated parent OPFRs, chlorinated OPFR products, non-chlorinated parent OPFRs and non-chlorinated OPFR products, respectively. Note that a lower fathead minnow LC50 indicates a higher toxicity. Compounds marked with asterisks are those identified in megacity field samples.
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Liu, Q., Li, L., Zhang, X. et al. Uncovering global-scale risks from commercial chemicals in air. Nature 600, 456–461 (2021). https://doi.org/10.1038/s41586-021-04134-6
Anthropocene Science (2022)