Pollution Characteristics And Risk Assessment Of Organophosphorus Esters In Paddy Fields Of Nanning City

Organophosphate esters（OPEs）,a type of flame retardants and plasticizers,are showing a wide range of applications as the most potential substitutes for phasing-out of brominated flame retardants in many countries in recent years.In most applications,OPEs are mainly used as noreactive additives in products rather than being chemically bounded to polymer matrix.Thus,they are liable to release to different environmental compartments via volatilization,leaching and/or abrasion durning their production,use and disposal.Among the OPEs,parts of them have been suspected to be carcinogenic,neurotoxic effects,allergenic effects,adverse effects on fertility,and so on,which may pose threats to human health through diverse routes,e.g.,dermal contact,dust ingestion,inhalation and dietary intake.Rice is one of the most widely cultivated staple foods in the world,especially in Asian countries.Moreover,rice consumption is a major pathway for human exposure to OPEs among the different food items.However,few studies have focused on the occurrence,behavior and fate of OPEs in paddy fields by now.In this study,the occurrence,composition profiles,urban-rural and seasonal distributions,behavior,and fate of eleven organophosphate esters（OPEs）were investigated among multiple matrices（air,rain,dustfall,paddy soil,irrigation water,and rice plants）in a subtropical paddy field,South China.The major results and conclusion are as follows:1.More than nine among the 11 target OPEs were detected in the seven 7 matrices.It indicated the wide occurrence of OPEs in the paddy field.The total concentrations of 11 OPEs(∑₁₁OPEs)in air,dustfall,rain,irrigation water,paddy soil,forest soil（background）and rice were in range（mean）of 24.7-1148（424）pg/m³,0.37-14.1（2.52）μg/g,3.61-192（84.2）ng/L,41.6-392（113）ng/L,0.04-5.48（2.07）ng/g,0.08-1.63（0.84）ng/g and 2.42-10.7（4.80）ng/g,respectively.∑₁₁OPEs was a little lower in the rain than in irrigation water.∑₁₁OPEs was significant higher in the paddy soil than in the background soil（forest soil）.2.In general,the compositins of OPEs in all types of samples were similar.Among all the individual OPEs,the sum of three chlorinated OPEs（∑₃Cl-OPEs）were all higher than the sum of eight non-chlorinated OPEs（∑₈NCl-OPEs）.The contribution of∑₃Cl-OPEs to∑₁₁OPEs in the seven types of samples ranged from 59.8%to 88.3%.TCIPPs was the most predominant contaminant in all the types of samples exculde the rice samples.Its contribution to the∑₁₁OPEs was in range of 44.4%-68.2%.3.∑₁₁OPEs in all kinds of matrices were higher in urban area than in rural area and were higer in summer than in fall season,indicating that urban area is the local source of OPEs;also,the temperature is an important factor affecting OPEs’s diffusion.4.Correlation analysis indicated that∑₁₁OPEs in air correlated to∑₁₁OPEs in other six matrices except irrigation water and∑₁₁OPEs in rice significantly positively correlated to∑₁₁OPEs air,dust,and paddy soil.5.The results of air-soil exchange,water-air exchange,and water-soil distribution demostrated that net deposition of OPEs from air to soil and water adsorption of OPEs from water to soil occurred most of cases.It indicated that air is a main source of OPEs in the paddy fields and the soil is a main environmental reservoir of OPEs.Input fluxes of OPEs via air-soil exchange,atmospheric deposition and irrigation water averaged 396,796 and 906 ng/m²/d,respectively.Output flux of OPEs via mature rice plants was 221μg/m²,which was similar to the sum of input flux through deposition and irrigation（169μg/m²）in a growing season（100days）and the decrease flux of OPEs in soil（about 86.3μg/m²）.Among the outout flux,more than half along with the rice plant roots were（127μg/m²）still keep in the soil and 1.7%were present in rice.6.The maximun OPEs exposures to adult throught rice dietary,inhalation,dust ingestion,and dermal absorption via dust were 51、0.26、7.2 and 0.035 ng/kg bw/day.Dietary exposure via rice was much higher inhalation exposure,dust ingestion,and dermal absorption vis dust.However,all the intake values via the four exposure paths could not pose risks to human health now.