Atmospheric Autoxidation of Organophosphate Esters

Abstract

Organophosphate esters (OPEs), widely used as flame retardants and plasticizers, have frequently been identified in the atmosphere. However, their atmospheric fate and toxicity associated with atmospheric transformations are unclear. Here, we performed quantum chemical calculations and computational toxicology to investigate the reaction mechanism of peroxy radicals of OPEs (OPEs-RO 2• ), key intermediates in determining the atmospheric chemistry of OPEs, and the toxicity of the reaction products. TMP-RO 2• (R 1 ) and TCPP-RO 2 • (R 2 ) derived from trimethyl phosphate and tris(2-chloroisopropyl) phosphate, respectively, are selected as model systems. The results indicate that R 1 and R 2 can follow an H-shift-driven autoxidation mechanism under low NO concentration ([NO]) conditions, clarifying that RO 2• from esters can follow an autoxidation mechanism. The unexpected autoxidation mechanism can be attributed to the distinct role of the (O) 3 P(O) phosphate-ester group in facilitating the H-shift of OPEs-RO 2• from commonly encountered OC(O) and ONO 2 ester groups in the atmosphere. Under high [NO] conditions, NO can mediate the autoxidation mechanism to form organonitrates and alkoxy radicalrelated products. The products from the autoxidation mechanism have low volatility and aquatic toxicity compared to their corresponding parent compounds. The proposed autoxidation mechanism advances our current understanding of the atmospheric RO 2• chemistry and the environmental risk of OPEs.

The driving effects of common atmospheric molecules for formation of prenucleation clusters: the case of sulfuric acid, formic acid, nitric acid, ammonia, and dimethyl amine

“…3,4 The precise way that gaseous vapor comes together to form prenucleation complexes, which eventually build to aerosols, and thus form CCN, is a very active area of research. 3,5–74 Much of this activity is driven by the uncertainty in how much aerosols and clouds will impact global warming. 75,76 While it is thought that in general more aerosols will lead to a cooling effect, the uncertainty in our knowledge exceeds the actual size of the predicted cooling.…”

Insights into the Atmospheric Persistence, Transformation, and Health Implications of Organophosphate Esters in Urban Ambient Air

“… 65 Cl- and aryl-OPEs have similar transformation pathways as alkyl-OPEs, but Cl atom in the C–Cl bond of Cl-OPEs can also be substituted by −OH. 26 , 31 …”

“…64 Cl-and aryl-OPEs have similar transformation pathways as alkyl-OPEs, but Cl atom in the C−Cl bond of Cl-OPEs can also be substituted by −OH. 26,31 The main plausible transformation products of OPEs from the proposed transformation pathways were screened in the particulate samples by QTOF−MS. In addition to the transformation products mentioned above, four other transformation products, that is, C 16 S10).…”

“…On the basis of the in silico prediction results, microbial biodegradation can also transform OPEs to diester or monoester and hydroxylated derivatives, as well as the derivatives containing −CO – , −CHO, or −COOH (Figures S7–S9), while hydrolysis usually generates diester and monoester derivatives and may play a minor role in the transformation processes of OPEs . Cl- and aryl-OPEs have similar transformation pathways as alkyl-OPEs, but Cl atom in the C–Cl bond of Cl-OPEs can also be substituted by −OH. , …”

“…Therefore, transformation products of OPEs may significantly contribute to ambient air pollution and increased health risk. Although bench-scale experiments and model simulations have been conducted to understand the kinetics and mechanisms of OPE atmospheric transformation, − the transformation potential and products of OPEs in ambient air remain largely unknown . Context-specific factors, such as meteorological conditions, radical abundances, and constituents of particles (e.g., microbes and metallic and organic species), can greatly influence the transformation processes in the air. ,, This complexity highlights the need to evaluate the persistence and transformation of OPEs in the natural atmosphere and potential health risks.…”