Research On The Distribution Of Phthalic Acid Esters (PAEs) Of Rice In The Pearl River Delta Region

In recent years, the environmental pollution problems caused by phthalic acid esters(PAEs) had aroused widespread concern. With wide use of PAEs in industry and large-scale application in plastic film mulching(including plastic greenhouses) for cultivation, agricultural soils were contaminated by PAEs. Currently, numerous investigations have been conducted about the pollution of PAEs on vegetables and soils, especially greenhouse cultivation, while research on rice-growing areas was rarely reported. Many studies have investigated the variation in the uptake and accumulation of PAEs by vegetables as well as their effect factors domestic and foreign. But the uptake pathways and mechanisms of PAEs by rice were rarely reported. In this study, to investigate the distribution of PAEs in paddy soils and grains of rice(Oryza sativa L.) in the Pearl River Delta region and to evaluate the human health risk of PAEs and bioaccumulation via the ingestion of rice, paddy soil samples(n=30) and grain samples(n=37) were collected from the rice cultivation areas of four cities(i.e., Dongguan, Guangzhou, Huizhou, Panyu) in this region. Nine PAE compounds in samples were ultrasonic-assisted extracted and analyzed using gas chromatography coupled with mass spectrometry(GC-MS). Additionally, two different genotypic cultivars of rice with PAE(phthalic acid esters) high-accumulation(cultivar Peizataifeng) and low-accumulation(cultivar Fengyousimiao) were grown in hydroponic systems contaminated with PAEs. The uptake pathways of PAEs by rice and its influencing factors were investigated to reveal the differences of high- and low-PAE accumulation of rice cultivars. The main results were as follows:(1) Di-n-butylphthalate(DBP), di-(2-ethylhexyl) phthalate(DEHP) and di-iso-butylphthalate(DIBP) were the most abundant compounds in paddy soil, accounting for more than 85% of the sum concentrations of nine PAE compounds(∑PAEs). The ∑PAEs in paddy soils ranged from 2.93 to 8.05 mg·kg-1 with a mean of 5.25 mg·kg-1, from 1.90 to 7.34 mg·kg-1 in roots, 3.37 to 6.65mg·kg-1 in stems, and 2.05 to 6.52 mg·kg-1 in leaves of rice. The highest average concentrations in both of paddy soil and rice plants were observed in the samples from Dongguan city. The bioaccumulation factor of various rice tissues to PAEs varied from 0.26 to 2.87, and translocation factor between 0.10 and 1.51, showing strong translocation capability for PAEs. Variation in accumulation of PAEs was observed by different cultivars of rice.(2) DBP, DEHP and DIBP were the most abundant compounds in grains. The ∑PAEs in grains were between 1.77 and 4.13 mg?kg-1 with a mean of 2.93 mg?kg-1. The highest average concentrations in grains(3.13±0.71 mg?kg-1) were also observed in the samples from Dongguan city. The bioaccumulation factor of grains to PAEs varied from 0.37 to 1.27, and some of them for DBP, DEHP and DIBP were greater than 1.0. The ∑PAEs in rice and chaff ranged from 1.32 to 3.22 mg·kg-1(with a mean of 2.17 mg·kg-1) and from 0.81 to 2.61 mg·kg-1(with a mean of 1.43 mg·kg-1), respectively. Estimated daily intakes of DBP and DEHP for adult via the ingestion of rice of this study ranged from 0.52 to 2.61 μg·kg-1-bw·day-1 and from 0.65 to 4.09 μg·kg-1-bw·day-1, those for child ranged 1.12 to 5.58 μg·kg-1-bw·day-1 and from 1.57 to 9.91 μg·kg-1-bw·day-1, being lower than the reference doses proposed by U.S. Environmental Protection Agency(DBP: 100 μg·kg-1-bw·day-1, DEHP: 20 μg·kg-1-bw·day-1). The human health risk via the ingestion of rice was relatively low.(3) The uptake pathways of PAEs in rice included root uptake, leaf absorption, transpiration pull and phloem migration were also the pathway for uptake of PAEs by rice. PAEs mainly distributed in cell walls, organelles, and only a small part in the cytoplasm. PAE stress had effects on the contents of low molecular weight organic acids of two rice cultivars, and then affected the uptake and accumulation of PAEs in rice plants. PAEs inhibited the synthesis of chlorophyll and affected on the photosynthesis of rice. However, the physiological characteristics of two rice cultivars were affected by PAEs. The activities of polyphenol oxidase, peroxidase, superoxide dismutase, catalase, malondialdehyde contents of two rice cultivars were affected by PAEs. Significant difference of enzyme activities was observed between the treatment with high PAE concentration and the control. Low-accumulation cultivar(Fengyousimiao) showed lower tolerance to PAEs than high-accumulation cultivar(Peizataifeng).