Impacts Of Glomalin-related Soil Protein On Sorption,Desorption And Availability Of PAHs In Soils

In China,the contamination of organic pollutants in soils is becoming a serious issue.How to enhance the prevention of contaminated soils and improve the environmental quality of soils have become a hot topic of concern worldwide.Among these organic pollutants,polycyclic aromatic hydrocarbons(PAHs)are a category of persistent organic pollutants that are of attention for the environment due to their potential to be strong carcinogenic and mutagenic properties.It is noted that arbuscular mycorrhizal fungi(AMF)can remediate PAH-contaminated soils and reduce the uptake of PAHs by plants,but its mechanism is not clear.Glomalin-related soil protein(GRSP),as soil organic material,was produced by the hyphae of AMF.Unfortunately,the effect of GRSP on the environmental behavior of PAHs in soils is scarce.Thus,understanding the impact of GRSP on sorption/desorption and availability of PAHs is vital for evaluating the remediation mechanism of PAH-contaminated soils by AMF.In this work,the sorption,desorption,and availability of phenanthrene and pyrene in three typical zonal soils were studied.The impact of GRSP on sorption and desorption of phenanthrene was investigated in soils using batch experiments.The effect of GRSP on the availability of PAHs was also performed using microcosm experiment methods.The primary results are exhibited as follows:(1)The impact of GRSP on sorption of phenanthrene was conducted in different soil types(i.e.,Kandiudult,Typic Paleudalf,Mollisols)by batch experiments.The sorption isotherms of phenanthrene by three tested soils were determined using a linear sorption model with correlation constants(r)bigger than 0.93 regardless of the GRSP presence.The transfer of nonionic chemicals from water to soil was described with a hypothesis of solute partitioning in the soil organic matter.The addition of GRSP impeded the distribution of phenanthrene in soils,and the larger GRSP amount added in soils,the stronger inhibition of phenanthrene sorption.For instance,the addition of GRSP resulted in the Kd value for phenanthrene sorption in Kandiudult,Typic Paleudalf and Mollisols decreasing from 286.35,294.91 and 313.91 L·kg-1 to 68.49,72.97 and 106.3 L·kg-1,respectively.Different types of GRSP had different effects on phenanthrene sorption,and the inhibition of T-GRSP on the phenanthrene sorption for all soil types was always greater than EE-GRSP.The Kd values of test soils after native GRSP removed were increased,indicating that the presence of GRSP impeded the phenanthrene adsorption by soils.The Kphen/GRSP and Kphen/doc were larger than the Kd.The addition of GRSP resulted in an increment of dissolved organic matter(DOM)concentration in solution.Phenanthrene in soil-water systems was more readily associated with DOM or GRSP in solution versus soil solids,resulting in the release of phenanthrene from soil solids into solution.This was also a dominant mechanism of the GRSP-enhanced PAH availability in soils.(2)The impact of GRSP on desorption of PAHs was also investigated in three tested soils(Kandiudult,Typic Paleudalf,Mollisols)by a batch approach.The data showed that GRSP significantly enhanced the desorption of phenanthrene and pyrene by soils.The increasing aging time decreased the desorption amounts of phenanthrene and pyrene.The lower soil foc value corresponds to the larger increment of PAHs desorption.The enhanced ability for PAHs desorption was in the order of T-GRSP>EE-GRSP.For example,the desorption amount of phenanthrene increased from 5.32 mg·kg-1 to 5.62 mg·kg-1 by adding 20 mg·L-1 T-GRSP;however,with the addition of 60 mg·L-1 EE-GRSP,the desorption amount of phenanthrene only raised from 5.32 mg·kg-1 to 6.44 mg·kg-1.GRSP enhanced the PAHs desorption likely due to the DOM concentrations of the solution increased with the larger of GRSP amount.(3)The impact of GRSP on the availability of PAHs was investigated in sterilized soils for 60 d incubation using microcosm experiment methods.We used the butanol extraction technique to evaluate the availability of PAHs in soil.Results indicated that the addition of GRSP(5?25 mg·kg-1)significantly increased the butanol-extractable amounts of phenanthrene in a concentration-dependent manner,and higher GRSP concentrations resulted in more extractable phenanthrene in soil.The concentrations of extractable phenanthrene in soil with 25 mg·kg-1 GRSP were 52.2?204.4%higher than GRSP-free,implying GRSP could significantly enhance soil PAH availability.The aging time,types of.PAHs and microbes also had an influence on the availability of phenanthrene and pyrene.The fraction of butanol-extractable phenanthrene and pyrene decreased 51.7%and 17.5%after 60 d anging.Pyrene was more difficult to be degraded because it has more benzene rings and a higher molecular weight.Microbes also had a strong influence on the availability of PAHs.