Biogeochemistry Processes Of Polycyclic Aromatic Hydrocarbons In Soil/Sediment-Organism Systems

Polycyclic aromatic hydrocarbons(PAHs),as a set of typical persistent organic pollutants,have been found in worldwide multimedia and are of great concern. Soil/sediment is an important sink of PAHs and organisms living in the soil/sediment are key media for PAHs transferring and accumulating through the food web. Therefore,conducting the present study has important theoretical significance for enriching PAHs biogeochemical researches.Moreover,the results will also improve the accuracy of ecological and health risk assessments and means of controlling PAHs pollution.The present study selected typical soil/sediment-organism systems.Then,the mechanisms of PAHs accumulation,transfer and biodegradation and its effecting factors were elucidated combining field survey and laboratory simulation methods and environmental geochemistry,agrology and biology subjects.Soil-rice system which the organisms living in is predominated by rice was selected as typical soil-plant system.The results showed that TPAHs levels in surface soils varied significantly in different sampling sites around Shanghai.All surface soils were prevalent of PAH(5+6)as about 43.4%of TPAHs while PAH(2+3)as the least compounds were only about 18.5%.TPAHs and individual PAH compounds levels had no significant correlation with soil physicochemical characteristics.In agriculture field,rice plant accumulated PAHs mainly through absorption and adsorption airborne PAHs by leaves.Another important organ for rice getting PAHs was root which can accumulate PAHs from soil.Stem and seed received PAHs depending on transfer from leaf and root.TPAHs and PAH compounds root accumulate factor were 0.05-0.08 and 0-0.41,respectively,which indicated that there was no biomagnification of PAHs by rice root through around soil.In both soil profiles before and after rice planting,TPAH and PAH compounds levels were gradually decreased with soil depth.The decrease was most significant between surface soil and sub-surface soil and pollution levels were getting steady in soils below 60 cm.There was obvious declination of PAHs levels in soil after rice planting.PA and PAH(4)were caught and enriched in sub-surface layer(10-20 cm) except of Nap after rice planting.PAH(2+3)levels decreased with soil depth,however, PAH(4)and PAH(5+6)showed opposite trends.SOC(soil organic carbon)was the most important factor affected PAHs transferring and accumulating.In contrast,BC (black carbon)was no significant relationship with PAHs soil mobility.Relative enrichment factor results suggested that PAHs occurred relative enrichment every other layer in soil profile before rice planting.However,the relative enrichment factors changed greatly after rice planting,which showed that rice planting was able to remove PAHs from soil profile and change the vertical variation of PAHs levels. Additionally,relative enrichment factors had no significant correlation with 1g K_OW in both soil profiles,indicating that PAHs behaviors in soil profile were not influenced by their physicochemical characteristics but other factors(such as eluviate and organism disturbing).Sediment-benthic animal system in winter from the Yangtze estuarine tidal flat was chosen as typical sediment-animal system because that benthic animals were majority in the system.The results suggested that TPAHs levels in surface sediment from the Yangtze estuarine tidal flat were from 87.7-1851.0 ng g^-1,averaged in 599.7 ng g^-1and decreased from inner to outer of the Yangtze river mouth.PAHs in surface sediments were dominated by PAH(4)and PAH(5+6).However,TPAHs levels in surface sediments from the Chongming island characterized by middle tidal flat＞high tidal flat＞low tidal flat.PAH(2+3)was the major PAH compounds.The relative content of PAH(5+6)decreased gradually from high tidal flat to low tidal flat.Source identification results showed that PAHs in surface sediments along the Yangtze estuary mainly came from incomplete combustion while PAHs in surface sediments from the Chongming island were mostly petrogenic PAHs.Tidal flat fish (periophthelmus cantonensis)from BLG site had the highest TPAHs level about 891.0 ng g^-1while crab(Sesarma)from Chongming middle tidal flat had the lowest level about 36.1 ng g^-1,which indicated that high trophic level animal tended to magnify PAHs concentration through food web.Crabs accumulated similar amount of PAHs, which was in relation to their hunting behavior and living habits.PAH(2+3)were the majority while PAH(4)was not found in all benthic animals' bodies.Lipid content may strongly control PAHs accumulation in benthic animals' bodies.PAHs levels and BSAF(bio-sediment accumulation factor)didn't vary according to PAHs levels and SOC in surface sediments.BSAFs of TPAHs and PAH(5+6)were lower which suggested benthic animals only had weak ability accumulating them from surface sediments.However,due to their higher water solubility,PAH(2+3) tended to be caught more by benthic animals,which caused higher BSAFs.In addition, BSAF had strongly correlation with LogK_OWWhen LogK_OW＜6,BSAFs increased according to LogK_OWwhile they decreased when LogK_OW＞6.Soil-microorganisms system in two sites along Mosel river was chosen as typical soil-microorganisms system because the soil was highly polluted by PAHs and microorganisms were the majority of organisms.Results showed that D₁₀-PA added to Temmels soil was biodegraded quickly about 92%and 99%during 2 and 4 weeks, respectively.Similarly,D₁₀-PA added to Konzerbr(u|¨)ck soil was biodegraded a large amount during 4 weeks,but the speed is only half of Temmels soil,which was in consistent with microorganism amount in two soil slurries.Bioavailable and killed control sets results for Temmels soil were compared and slight biodegradation was found.However,there was no significant biodegradation happened in Konzerbr(u|¨)ck soil.TPAHs had been biodegraded about 20.0±2.7 mg kg^-1in Saar coal control of Temmels soil.That is,19.0%of initial TPAHs in Saar coal control of Temmels soil was biodegraded,which indicated that PAHs of fresh Saar coal could be biodegraded by native microorganisms in Temmels soil.For Konzerbr(u|¨)ck soil,there was 46.0±1.1 mg kg^-1PAHs biodegraded in its Saar coal control.That is,31.5%of initial TPAHs in Saar coal control of Konzerbr(u|¨)ck soil,which was greatly contrary to its bioavailable set.This showed that extra Saar coal also could improve PAHs bioavailability in Konzerbr(u|¨)ck soil.However,extra Novgorod coal didn't increase PAHs biodegradation in Temmels soil.For Konzerbr(u|¨)ck soil,extra Novgorod coal led to 20.4%of initial TPAHs level.Compared to its Saar coal control,Novgorod coal control for Konzerbr(u|¨)ck soil biodegraded less PAHs,showing native microorganisms were not used to immigrant coals but native coals. For Temmels soil,the order of contribution to total biodegradation of PAH compounds in Saar coal control was PAH(2+3)＞PAH(5+6)＞PAH(4).Nap,1-MNap and PA had been biodegraded more in comparison of other PAHs.The order of contribution in Saar coal control and Novgorod coal control of Konzerbr(u|¨)ck soil had the same trend:PAH(2+3)＞PAH(4)＞PAH(5+6).Nap,1-MNap,2-MNap and PA were easiest to be biodegraded in Saar coal control while Nap,1-MNap and PA were biodegraded strongest in Novgorod coal control.