Health Risk Assessment Research Of Static Dust Impacting On Breathing Exposure Way

An abandoned chemical plant which located in central Hunan Province was chosen to investigate the the health risks of Cadmium(Cd), Arsenic(As), Chromium(Cr), Nickel(Ni) and Mercury(Hg) in surface soils. In order to research the static dust, its influence on breathing exposed way and its hazards to human health around the typical open-air industrial pollution area, a predict model of PM10 concentration near the ground was proposed, basing on the two phase gas-solid aerodynamic theory. Hence, this paper provided theoretical basis for soil pollution prevention and governance of the factory and sandland areas, and then it promoted parameters determination of health risk assessment.(1) The features of heavy metal concentration and vertical distribution of surface soil in contaminated site: The average concentration of Cd, As and Hg were exceeded the national standard(GB15618-1995) and Hunan Province background values. The concentration of As was the highest, Cd comes second, with both over standard rate above 58.54%, and parameter variations and coefficient of variability(CV) values of Cd, As and Hg were relatively large. In the same soil depth(0~2.0 m), Cr, As and Hg of the factory were higher than sandland area. The vertical distribution of heavy metals(except for Ni) was decreased with depth. Howerver, some heavy metals were increased or sustained with depth.(2) PM10 of near-soil-surface was significant influenced by meteorological factors such as wind direction and wind speed. In summer, PM10 concentration of residential area and commercial district which located on north of factory was reached 0.30mg/m3, with S, SSE and SSW wind and large wind speed. Likewise, PM10 concentration of tourist area was over 0.15 mg/m3 influcing by NW and NNW wind throughout the year. PM10 near the factory and sandland areas was the highest, and decreased rapidly with diffusion distance.(3) Exposure assessment results of respiratory pathway based on human body characteristics, time activity and intake rate showed that daily exposure(ADI) was directly proportional to PM10, but was inversely proportional to diffusion area. Therefore, people neare the pollution area were vulnerable with acquiring large ADI. Due to the characteristic, behavior, living habit, et al., the children has higher ADI than adults, and possessed more vulnerable to hazards than adults.(4) The monomial non-carcinogenic hazard quotient(HQ), the total hazard index(HI) and lifetime cancer risk(R) of heavy metal had a linearly relationship with PM10 which produced nearby pollution sources and influnced by wind.The results of health risk assessment show that the non-carcinogenic risk of Cd and As, which respectively have more than 56.73% and 37.78% contribution rate to the total hazard index(HI), exceed the acceptable risk(1) when the PM10 concentration is more than 0.125 mg/m3, 0.175 mg/m3, respectively. The carcinogenic risk of Cd, As and Cr exceed the acceptable risk(10-6) when the concentration of PM10>0.050 mg/m3, and carcinogenic risk level was As>Cr>Cd.The HI and R of children were higher than that of adults. Children possessed carcinogenic risks of Ni when the PM10 achieve 0.400 mg/m3, howerver, adults possessed low risk level.(5) HQ's and R's probability distribution of Cd, As, Cr, Ni and Hg of two kinds of exposed people were approximate. Probability of Cd and As in the safety threshold were 69% and 61%, repectively, and other 3 kinds of heavy metals' distribution was 100%.Four kinds of heavy metals which have without threshold carcinogenic risk were all over the threshold(10-6) probability distribution, with reliability respective reached 53%, 84%, 96%, 4%. The concentrations of heavy metals and PM10 were the significant factors which effect daily dose, non-carcinogenic risk level and lifetime cancer risk level by respiratory pathway into the unit body weight. Therefore, heavy metals in the pollution soil must be controlled and governed for prevention risk accident.(6) Based on the risk assessment of contaminated site, risk control values, which calculated by inversion computation inversion, of Cd, Cr, As and Ni were 2.13 mg/kg, 0.046 mg/kg, 0.89 mg/kg and 10.15 mg/kg, respectively.