Bioaccessibility And Influencing Factors Of Hydrophobic Organic Contaminants In Airborne Particles

Humans may expose to atmospheric particulate matter(PM)occupationally via oral and inhalation routes.The hazardous substances,such as hydrophobic organic contaminants(HOCs),are released into human body fluids from the particles and endanger human health.Based on the particle size,PM can be classified into inhalable and respirable particles.Bioaccessibility of HOCs was regarded as 100%in previous risk assessment research.It may overestimate the risk associated with exposure to HOCs,because the HOCs in particles could be influenced by its physicochemical properties and composition of particles and the release was rate-limited before the particles were eliminated from the body.However,there was lack of suitable gastrointestinal digestion model for atmospheric particulate matter,and the degree of HOCs released in the digestive tract was a gap in the research of bioaccessibility.Bioaccessibility of heavy metal in particles had attracted broad attention in the previous in vitro lung model research,while the bioaccessibility of HOCs had not been reported yet.The types and activity of active substances which were added in the simulation fluids,such as enzymes and bile salts,were inconsistent with human physiology and it may influence the bioaccessibility results of contaminants,especially for the HOCs.In addition,there was few research focusing on the effect of size and organic matter composition of particles on the bioaccessibility of HOCs.To understand the influence of external conditions and particle properties on the HOCs bioaccessibility and reveal the mechanism of influence,it is necessary to establish a respiratory and gastrointestinal digestion model that can be used in atmospheric particlesIn the research of gastrointestinal digestion model,the effects of pepsin activity,pancreatin type and activity,concentration and type of bile salts on the bioaccessibility of HOCs in PM were investigated.Rational parameters were established by comparing and analyzing the results between human physiological and previous parameters.In addition,the bioaccessibility of HOCs in inhalation routes was focused on our research including the influence of residence time,composition of simulated lung fluids.We observed some of OPFRs degradation in the simulated lung fluid.Spiking experiments were carried out to verify the results and reveal the mechanism of degradation.Particulate matter from eight typical environments in Guangzhou was collected to explore the influence of the intrinsic properties of the particle on the HOCs bioaccessibility,such as particle size and organic matter composition.Furthermore,we assessed health risk level of citizens in sample sites associated with environmental exposure to polycyclic aromatic hydrocarbons which combined with PAHs concentration and bioaccessibility simulation results.Pepsin and pancreatin activity can influence the bioaccessibility of HOCs in gastrointestinal digestion model.As pepsin activity increased,the bioaccessibility of HOCs rised slightly.Commercial pancreatin resulted in higher bioaccessibility of HOCs than pancreatin which composition was based on human pancreatic enzyme activity.Bile salts were important for greatly promoting the release of HOCs in atmospheric particles.When the concentration of bile salts was higher than its critical micelle concentration(CMC),bile salts molecules would gather and form micelles to promote the release of HOCs.Porcine bile salts which major components were inconsistent with human ones would result in lower bioaccessibility of HOCs than the bovine bile salts which components were similar to human.High-carbohydrate and protein diets can increase the bioaccessibility of HOCs,while green tea which was rich in catechin can compete with HOCs to bind with bile salts micelles in intestine and reduce the bioaccessibility of HOCs.When the bile salts concentration was 3 g/L,the bioaccessibility of HOCs was not significantly enhanced by liquor.However,when the concentration of bile salts was under its CMC,the promoting effect of liquor on HOCs was obvious.In inhalation route,only PAHs and OPFRs were bioaccessible and the release rate of most compounds were low.HFRs almost had no bioaccessibility with an extremely high log Kow value.With the simulation time extension,bioaccessibility of most HOCs increased.However,for the ClOPFRs,bioaccessibility peaked in the initial stage of the simulation.The bioaccessibility of HOCs in ALF fluid was significantly higher than that of GS solution,but the gap of bioaccessibility in the both fluids tended to be consistent as simulation time increased.DPPC can reduce the release of HOCs in GS fluid.TPhP,EHDPP and TCrP were degraded in GS fluid in the final phase of simulation.Spiking experiments were carried out and revealed that the half-life of these OPFRs ranged from 17 to 90 days.The mechanism of degradation was a nucleophilic addition and elimination reaction under the alkali-catalyzed.Fine particles(PM2.5),57.3%of the total suspended particles on average,were the main type of particles in each sample sites.PAHs was the major HOCs in particles at each sample sites,followed by the OPFRs.The concentration of HFRs was relatively low.Five and six-ring PAH and ClOPFRs,TPhP were major compounds in HOCs.Source apportionment of PAHs showed that biomass combustion was the primary source in most sample sites,while PAHs in PCP was mainly from fossil fuel burning.The bioaccessibility of PAH and HFR compounds tended to be consistent in the gastrointestinal digestion both for coarse and fine particles.However,for OPFRs,bioaccessibility significantly decreased as the log Kow value of compounds increased.Bioaccessibility of PAHs and OPFRs in fine particles was 2-fold and 4-fold respectively of that in coarse particles,but there was no uniform pattern for HFRs.OC concentration in particles was the significant factor which affected the bioaccessibility of HOCs greatly.The bioaccessibility of PAHs and OPFRs in the low OC group was 2-3 folds and 2-4 folds respectively of that in the high OC group.Correlation analysis showed that most PAH compounds and OPFRs with high log Kow value had strong negative correlations with OC concentration in fine particles.However,under the influence of particle size,statistically significant correlations were not found between bioaccessibility of HOC compounds and OC concentration in coarse particles.The rule found in fine particles was applicable for the inhalation simulation,but the OC concentration only showed strong negative correlations with HOC compounds which log Kow value was between 3 to 6.Risk assessment of PAHs exposure showed that the BEQ value of PAHs at the sample sites was 3 to 10-fold over the National Ambient Air Quality Standards.Among.them,petrochemical plant and wastewater treatment plant are the most polluted areas by polycyclic aromatic hydrocarbons.The PAHs average daily dose of citizens at each site was all under the EPA standard and loss of life expectancy(LL)was from 0.11 to 2.08 min for the sample sites.When the bioaccessibility was taken into consideration,the LL results were under 0.16 min.The human lifetime lung cancer risk in the sample sites was in tolerable range when the bioaccessibility was taken into account.Hence,bioaccessibility of HOCs was an important correction factor for risk assessment,which played a role in improving and optimizing the assessment results.