Uptake, translocation, bioaccumulation, and bioavailability of organophosphate esters in rice paddy and maize fields.

Rice and maize are two main crops with different growth habits in Northeast China. To investigate the uptake, translocation, and accumulation of organophosphate esters (OPEs) in those two crops, we measured the OPE concentrations in their agricultural soil-crop systems during different growing seasons. OPE concentrations were higher in paddy (221 ± 62.0 ng/g) than in maize (149 ± 31.6 ng/g) soil, with higher OPE levels in the rhizosphere than in bulk soil for rice, and the opposite in maize. Two-step extractions were used to obtain the labile and stable adsorption components of OPEs. The stable-adsorbed OPEs were activated to be more bioavailable by root exudates as rice grew. OPEs in rice increased linearly with the growing period. The uptake and translocation processes of OPEs by crops were not well-explained by logKow alone, indicating other processes such as growth dilution are significant for understanding OPE levels in plant. The translocation factors of OPEs from nutritive to reproductive organs indicated that OPEs in rice seeds may follow the translocation from root to leaf and then transfer to grains. Two genera, Sphingomonas and Geobacter, associated with degradation of organophosphorus compounds were enriched in rhizosphere soils, indicating enhanced OPE degradation.

Characteristics and risk assessment of organophosphate esters and phthalates in soils and vegetation from Dalian, northeast China.

We investigated the concentration, composition, and potential risk of organophosphate esters (OPEs) and phthalates (PAEs) in soils and vegetation from rural areas of Dalian, Northeast China. The residues of total OPEs and PAEs in soils were in the range of 33.1-136 ng/g dw (dry weight) and 465-5450 ng/g dw, while the values in plants were 140-2360 ng/g dw and 2440-21800 ng/g dw, respectively. The concentrations of both chemicals in the plant rhizosphere soils were significantly lower than those in the bulk soils, suggesting an enhanced degradation or uptake by plant. The contaminations in soils also varied for different land use types with the concentrations generally higher in paddy soils than those in maize soils. The OPE and PAE concentrations in plant leaves were slightly higher than those in their corresponding roots. The bioconcentration factors of OPEs & PAEs were significantly negatively correlated with their octanol-water partition coefficients. A hazard assessment suggested potential medium to high risks from tricresyl phosphate (TMPP) and di-n-butyl phthalate (DNBP) for the agricultural soils in Dalian of China. Although the ecological risks of OPEs and PAEs in the rhizosphere soils were lower than those in the bulk soils, the relevant risk could still endanger human health via oral intake of these plants. The daily dietary intakes of OPEs and PAEs via vegetable and rice consuming were estimated, and the result suggests a higher exposure risk via ingestion of leafy vegetable than rice.

Distribution of organophosphate esters between the gas phase and PM2.5 in urban Dalian, China.

We investigated the concentrations and seasonal variations of organophosphate esters (OPEs) in the gas phase and PM2.5 (particulate matter with an aerodynamic diameter <2.5 µm) in an urban area of Dalian, China, as well as their gas-particle partitioning. The total concentrations of OPEs in the gas phase were in the range of 0.056-6.38 ng/m3 with the mean concentration of 0.83 ± 1.24 ng/m3, while the concentrations of OPEs in the PM2.5 were in the range of 0.32-3.46 ng/m3 with the mean concentration of 1.21 ± 0.67 ng/m3. Tris-(1-chloro-2-propyl) phosphate (TCIPP) was the dominant congener in the gaseous phase, followed by tris-(2-chloroethyl) phosphate (TCEP) and tri-n-butylphosphate (TNBP), whereas TCEP was the dominant species in the PM2.5, followed by TCIPP and triphenyl phosphate (TPHP). Seasonality was discovered for OPEs in both gas phase and PM2.5 with their concentrations higher in hot seasons, which may due to the temperature-driven emission or gas-particle partitioning. The PM2.5-bound fractions of OPEs varied significantly between seasons. Tricresyl phosphate (TMPP), tri(2-ethylhexyl) phosphate (TEHP), 2-ethylhexyl diphenyl phosphate (EHDPP), and TPHP were mostly adsorbed onto fine particles, while TNBP, TCEP, TCIPP, and tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) distributed in both gas and fine particle phases. The predicted PM2.5-bound fractions by Koa-based model were closer to the measurements for TCIPP, TDCIPP, and TPHP, whereas the predictions by Junge-Pankow model were closer to the measurements for TMPP and tris (2-butoxyethyl) phosphate (TBOEP). However, the predictions of both models cannot accurately match the measured gas-particle partitioning of TNBP and TCEP.

Polycyclic aromatic hydrocarbons in the atmosphere and soils of Dalian, China: Source, urban-rural gradient, and air-soil exchange.

We investigated the concentrations, distributions, and sources of PAHs in the air and soils of Dalian, China, as well as their air-soil exchange trends. Total concentrations of PAHs in the air ranged from 6.37 to 124 ng/m3 with an average of 23.1 ± 26.6 ng/m3, while Σ15PAHs in the soils ranged from 42.8 to 28600 ng/g with an average of 2580 ± 5730 ng/g. Significant spatial distribution of PAHs was discovered in the soils with a clear urban-suburban-rural decreasing gradient, suggesting urban area is more contaminated by PAHs due to frequent and intensive human activities. However, high PAH concentrations were also discovered in the air from several rural sites, implying some PAH sources have shifted from urban to suburban or rural areas. Source apportionment indicated that major sources of PAHs in the urban and suburban soils were traffic emission/oil spill and coal combustion respectively, whereas major sources in the rural soils were diverse. Air-soil partitioning result suggested that 3-ring PAHs were mostly volatilized from soil, 6-ring PAHs were deposited into soil, while the trends of 4∼5-ring PAHs varied with sampling site. Fluoranthene, Pyrene, and Chrysene were mostly discovered to be volatilized in the urban and suburban areas, but equilibrium or deposited in the rural area, indicating a potential urban-to-rural transport of PAHs. The atmospheric transport and source shift of PAHs from urban to rural areas highlighted the importance of PAH source control on a regional scale.

Characteristics and risk assessment of organophosphorus flame retardants in urban road dust of Dalian, Northeast China.

We investigated the occurrence, distribution, and potential sources of 10 organophosphorus flame retardants (OPFRs) in road dust from the urban area of Dalian, China, as well as their associated human exposures and health risks. The total concentration of Σ10OPFRs ranged from 300 to 7480 ng/g with a median of 1600 ng/g. Relatively high concentrations were observed mainly near prosperous business districts or dense residential areas. Tris(2-chloroethyl) phosphate (TCEP), tris(1-chloro-2-propyl) phosphate (TCIPP), and triphenylphosphine oxide (TPPO) were detected in all dust samples. TCIPP was the dominant congener, followed by TPPO. It was found that traffic flow can obviously influence the concentration of OPFRs in road dust, suggesting vehicles may be the major sources of OPFRs in road dust, presumably from materials used in their interiors. Correlations between certain OPFRs and population density indicate a significant influence by anthropogenic activities on OPFR levels. The average daily doses (ADD) of Σ10OPFRs via ingestion, inhalation and dermal absorption from road dust were evaluated as 0.26 and 0.087 ng/(kg-bw·d) for children and adults respectively, with dust ingestion as the main exposure pathway of OPFRs. Although the exposure risk of OPFRs via road dust was relatively low in Dalian, further studies on the exposure of OPFRs are still necessary due to combined effects with other exposure pathways.