Organophosphite Antioxidants in Mulch Films Are Important Sources of Organophosphate Pollutants in Farmlands

Organophosphite antioxidants (OPAs) are important auxiliary antioxidants used in plastic polymers and can be oxidized to organophosphate esters (OPEs) during production and processing. In this work, the occurrence of OPAs and OPEs in farmlands with or without mulch film applications was investigated. Six OPAs and five OPEs were detected, with the median concentrations of 2.66 ng/g (Sigma 6OPAs) and 100 ng/g (Sigma 5OPEs) in the film-mulching soil and 1.16 ng/g (Sigma 6OPAs) and 47.9 ng/g (Sigma 5OPEs) in the nonfilm-mulching soil, respectively. The oxidative derivative of AO168 (tris (2,4-di-tert-butylphenyl) phosphite), a typical OPA, AO168=O (tris (2,4-di-tert-butylphenyl) phosphate) was frequently detected in farmlands at the concentrations of 0-731 ng/g, which is much higher than that of the commercial OPEs (0-12.1 ng/g). This suggests that the oxidation derivatives of OPAs (OPAs=O) might be important OPE contaminants in soils. Mulch films could be their important source. According to the simulation migration experiment, the emission risk ranges of AO168 and AO168=O from mulch films to soils in China were estimated to be 3.96-87.6 and 10.5-95.3 tons/year, respectively, which were much higher than those of OPEs from sewage sludge applications. Simulation experiments also demonstrated that oxidation was the major pathway for OPAs in soils. OPAs with small substituent groups could be potential sources for organophosphate diesters. For the first time, the serious pollution of OPAs and OPAs=O in soils has been reported, and mulch films have been identified as their potential source.

Automated summary

The study found that organophosphite antioxidants and organophosphate esters were present in farmland soils, with the oxidation derivatives potentially being important contaminants. Mulch films were identified as a potential source for these compounds, with oxidative derivatives of OPAs being more prevalent in soils compared to commercial OPEs.