| Hydrophobic organic chemicals(HOCs)in soil could be accumulated in organism and plants.It is necessary to develop a method for simultaneously determining the bioavailability of HOCs in soil for organism and plants.Passive sampling techniques have been widely applied for assessing the bioavailablity of HOCs in sediments,but limited in soils.In addition,soil has a unique three-phase structure of gas,liquid,and solid.There is a challenge on evaluating the contributions to HOCs accumulation on the passive sampler from their gaseous and dissolved amounts in soils.Therefore,a passive sampling device with polydimethylsiloxane(PDMS)as the adsorption phase was firstly developed for measuring the bioavailable HOCs in the present study.Second,a model was established for the evaluating the contributions to HOCs accumulation on the passive sampler from their gaseous and dissolved amounts in soils.Finally,two typical hydrophobic organic pollutants(HOCs),polybrominated diphenyl ethers(PBDEs)and organic phosphorus flame retardants(OPFRs),were used as target compounds.With carrot,lettuce and earthworm as a biological subjects,the feasibility of the passive sampler to assess the bioavailability of typical hydrophobic organic pollutants in soil was validated through a series of laboratory tests.The main results are summarized as follows.Firstly,we calculated the ma/mw value of organic pollutants in soil pore water and pore gas diffusing into PDMS adsorption phase by using Fick's first diffusion law and combining the diffusion coefficient and Henley coefficient and other relevant influencing factors.At the same time,by means of orthogonal analysis,it can be inferred that the environmental factor with the greatest influence on ma/mw value is temperature,followed by the water-gas volume ratio in the soil pores,and the least influence factor is the salt content of pore water and air pressure.Secondly,a plant and benthic culture device was designed and developed to detect the bioavailability of PBDEs and OPFRs in lettuce and carrots in the soil,and a passive sampler of soil organic pollutants was placed in the culture device for assess the bioavailability of soil organic pollutants.The results showed that compounds with low log Kow value were more likely to migrate from the soil into lettuce leaves and carrot taproots,and this phenomenon was more obvious in PBDEs compounds.The concentration of BDE-15 in the edible part of vegetables more than 75% of the total concentration of PBDEs compounds.In comparison,a large number of compounds with low log Kow values in OPFRs were not detected in the edible part of vegetables.For example,TCEP was not detected in the low-concentration experimental group,while the detected amount in the high-concentration experimental group was less than 1% of the total concentration of OPFRs.In addition,we will take the logarithm of the concentration of the target substance in the passive sampling adsorption phase and the vegetable edible part and then conduct correlation analysis.The compounds of PBDEs in the edible part of vegetables showed strong correlation.OPFRs compounds also show similar characteristics,but some of them showed weak correlation,which may be related to the degradation of OPFRs by plants.In general,the passive sampling technique can effectively assess the bioavailability of typical organic pollutants in soil.Finally,we use the calculated ma/mw value to calculate the mass concentration of the target substance loaded from the pore water on the PDMS adsorption phase,and use this mass concentration and the concentration of the corresponding compound in the biological phase to take a logarithmic value for correlation analysis.The results show that the use of the target concentration in the pore water obtained after the ma/mw value correction can effectively evaluate the bioavailability of typical hydrophobic organic pollutants in the soil.This method can effectively reduce the overestimation of the bioavailability of soil typical organic pollutants by PDMS. |
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