Study On Pollution And Risk Assessment Of Heavy Metals Surrounding Electroplating Plants In Dongguan

Since the adoption of reform and opening-up policy, China’s electroplating industry has achieved rapid development, regardless of the size, yield or output value has entered among the world’s electroplating powers. The rapid development of the electroplating industry stimulates the economic development of other areas. With the eight industries which were electronic information manufacturing industry, electrical machinery manufacturing, textile and garment manufacturing industry, furniture manufacturing industry, toy manufacturing industry and so on were established as a pillar industry in Dongguan in 2005, the scope of electroplating process was constantly expanding, however, electroplating enterprises discharge a large amount of exhaust gas, waste liquid and waste residue which is harmful to the environment and human health in the production process, which has been widely concerned. But previous research is more concerned about electroplating wastewater treatment and the heavy metal pollution of relocated electroplating site, seldom concerned about the pollution of heavy metals in the surrounding environment of electroplating enterprises. Therefore, the main research of this paper aims to the pollution characteristics of the heavy metals and the impact on the ecological environment and human health in the environmental medium around the electroplating factories in Dongguan, and we also mainly discussed the migration regularity of heavy metals in the multiple ambient medium of soil-rice and surface water-sediment system in the key research area Changan Town surrounding electroplating factories. The main results are as follows:1. Study on pollution characteristics and risk assessment of heavy metals in soil around electroplating plants(1) The pH average values of surface and shallow soil around the 42 electroplating factories in Dongguan were 6.18 and 6.13, respectively, which showed that the soil had been polluted by acid to a certain degree. Compared with the background value of soil in Guangdong province, Cd, Cu, Hg, Ni, Pb and Zn had been enriched to a certain extent, the average concentration of Hg in surface soil exceeded the secondary soil environmental quality standards (GB156182-1995). Except Cd, the spatial distribution of heavy metals in study area showed that concentrations of heavy metals in the surface soil were higher than shallow soil.(2) The single factor pollution index showed that Hg was polluted heavily in soil of the study area, and concentrations of Cu, Hg and Ni in partial sampling positions were exceeded the standard limits greatly. Nemerow pollution index showed that the pollution levels of heavy metals in surface and shallow soil were both serious, and the pollution of heavy metals in surface soil was worse, the PN values in surface and shallow soil were 6.87 and 4.71, respectively. The results of geo-accumulation index showed that Hg, Cd, Cu and Pb in surface and shallow soil were all influenced by human activities to some extent. Hg in surface soil was moderate pollution; Cd, Ni, Cu and Pb were light-moderate pollution; The rest elements were non-pollution.(3) Speciation analysis of heavy metals from 8 surface soil samples indicated that As, Cr, Cu, Hg, Ni, Pb and Zn were mainly associated with the residual fraction. The maximum content of the acid extractable for Cd was up to 34.48% in S5 sampling point, it was polluted seriously by human activities, with the high level of ecological risk. The bioavailability evaluation of 8 surface soil samples in study area showed that potential ecological risk of heavy metals decreased as followed:Cd>Pb>Hg>Zn> Ni>Cu>As>Cr.(4) The results of potential ecological risk index showed that the potential risk level of Hg in surface soil was very high, Cd was middle, and the rest elements of Ni, Cu, Pb, As, Zn, and Cr were light. Hg and Cd were the main factors of the potential ecological risk in soil of the study area. The RI values of total potential ecological risks of elements in surface soil of 5 towns followed the order:Machong> Dalingshan> Humen> Shatian> Changan, which showed that the risk level of Machong was very high, however, the risk levels of Dalingshan, Humen, Shatian and Changan were high.(5) The results of non-carcinogenic risk assessment showed that the oral intake was the mainly exposure way in surface soil of the study area. The health risk of As was highest, and the average value of HQois value was 1.46. The average values of HQdcs through skin contact exposure way were all under 1, while the maximum HQpis value of Ni through inhalation exposure way was 5.04. In addition, the average HIT value of heavy metals in surface soil of study area was 4.95. The contribution rates of As, Cr and Pb to the total risk were 38.39%,24.19% and 22.12%, respectively, and their cumulative contribution rate reached up to 84.70%. It showed that As, Cr and Pb were the major non-carcinogenic factors. The results of the carcinogenic risk assessment showed that Cr and As through three kinds of exposure pathways were higher than other metals, the CR values of Cr and As were all greater than 1× 10-6. The mean CRT value of heavy metals in surface soil of the study area was 1.87E-04, which was higher than 10-4, it indicated that the carcinogenic risk which caused by heavy metals in surface soil was seriously. The contribution rate of Cr and As to the total carcinogenic risk were 89.23% and 10.45%, the cumulative contribution rate of both was more than 99%.2. Study on pollution characteristics and risk assessment of heavy metals in surface water around electroplating plants(1) Comparing with the Class III limit value of Surface Water Environmental Quality Standards(GB3838-2002), the four seasonal average concentrations of As, Cd, Cr, Cu, Pb and Zn in surface water of the study area were all under the limit value, while Hg and Ni exceeded the corresponding standard limit values were 3.50 and 7.84 folds, respectively. The average contribution rate of Zn to the total concentration of heavy metals in sampling points was the highest, followed by Ni, Cu and Cr. Heavy metals in surface water showed the characteristics of seasonal distributions, and the change trend was inconsistent, the seasonal variation of Zn, Ni and Cu was most obvious, followed by Cr and Hg, Cd, while the seasonal characteristics of Pb and As were no significant.(2) The single factor pollution index showed that the pollution of Hg and Ni were serious in four seasons in surface water of the study area. Nemerow pollution index of heavy metals in 5 towns showed that the pollution level of Dalingshan was slight, Machong was moderate, while Shatian, Humen, Changan were seriously pollution. The PN values of heavy metals showed that As, Cd, Cu reached the safety grade, Pb and Zn reached the clean grade, and Cr reached the light grade. The PN values of Hg and Ni were 4.21 and 13.39, both were greater than 3, so the surface water in study area was polluted seriously.(3) The results of ecological risk assessment by the SSD method showed that Cu had the highest PAF value, followed by Zn, while the ecological damage degree of Cd, Pb and Hg was lower. The range of mean msPAF value of Cd, Cu, Hg, Pb and Zn in four seasons of the study area were between 15.41%～90.79%, and the total mean msPAF value was 45.72%. Compared with the msPAF values between four seasons, In spring, the msPAF value was highest (48.55%). And the PAF values of Cu and Zn contribute to the msPAF values both played an important role in four seasons of the study area.(4) The results of health risk assessment showed that the health risks of 8 metals in study area followed the order:Cr> As> Cd> Pb> Ni> Cu>Hg>Zn, and the personal annual risk caused by heavy metals through drinking water pathway were all greater than the skin contact way, in addition, the mean personal annual health risk for children were higher than adult caused by heavy metals through drinking water and skin contact pathways. The Ri values of Cr through drinking water pathway were all more than 10-4 a-1, the carcinogenic risk was high. The child Ri value of As through drinking water pathway was 1.62 times higher than the recommended value of ICRP. In addition, the total health risks produced by carcinogenic metals of As, Cd and Cr were between 1.24E-04 and 4.32E-03 a-1, with a mean value of 8.17E-04 a-1, while total health risks produced by non-carcinogenic metals of Cu, Hg, Ni, Pb and Zn were between 3.03E-09 and 7.04E-08 a-1, with a mean value of 1.56E-08 a-1. The health risk values of carcinogenic metals were 4-5 orders of magnitude as much as the non-carcinogenic metal. Compared uncertain health evaluation with deterministic health evaluation, the results showed that the evaluation level of the undeterministic model was generally higher than the deterministic model in study area. By the undeterministic model can more accurately reflect the real heavy metals pollution situation of surface water.3. Study on pollution characteristics and risk assessment of heavy metals in atmospheric particulate matters around electroplating plants(1) The four seasonal average concentrations of PM2.5, PM10 and TSP were 71.26 μg/m3,87.31 μg/m3 and 271.76 μg/m3, respectively, which were all less than daily mean value of the grade II air quality standard (GB3095-2012). The average over standard rate of PM2.5 was 42.2%, TSP was 26.7%, PM10 was conform to the standard. Furthermore, the rules of seasonal change for 3 kinds of particles in 5 towns were similar. And these 3 kinds of particles pollution were the most seriously in winter and the least in summer.(2) Comparing with the annual mean concentration limit value of Air Quality Standard (GB 3095-2012), the average concentrations of As, Cd and Cr of PM2.5, PM10 and TSP exceeded the limit values, while Hg and Pb were both under the limit values. The content ratio of PM2.5, PM10 and TSP showed that heavy metals were easy to gather in PM2.5. The seasonal distributions of 3 kinds of particles were similar with their mass concentrations. The concentrations of the most heavy metals were much more higher in winter and lower in spring and summer.(3) In study area, the enrichment characteristics of each element was similar in 3 kinds of particles. Cr, Ni and V were not enriched in 3 kinds of particulate matters. The EF values of As, Co, Cu, Pb and Zn was between 5 and 40, which were probably from natural source and the superposed of industrial pollution. In addition, the EF values of Cd, Hg and Sb were over 40, which indicated that these elements were seriously polluted by human activities. The Igeo values of Cr, Mn and V were less than 0 which showed that these elements were not polluted, which mainly came from the effect of natural factors. ButNi, Co, Cd, Hg, Sb, Pb, Zn, As and Cu were mainly affected by human activities, so the pollution degree was heavy.(4) The chemical speciation analysis of atmospheric particulate matters in autumn showed that except As, Co, Cr, Mn and V, most of heavy metals such as Cd, Cu, Sb, Pb, Ni and Zn mainly existed in acid extractable. Biological effectiveness evaluation showed that Cd, Sb, Cu, Zn, and Pb were available elements, and Ni, Hg, Mn, Co and As were potential biological availability elements, while V and Cr were biological unavailable elements.(5) The potential ecological risk index of Cd, Hg, As, Pb in PM2.5, PM10 and TSP of the study area were higher than 320, and the potential ecological risk was extreme. The RI values of heavy metals in atmospheric particulates of all sampling points in the study area were far more than 600, with ecological risk very high. And Hg and Cd made higher contribution rates to RI values. The non-carcinogenic exposure risk values of Mn were 1-4 orders of magnitude as much as the other metals in three aerosol particles of the study area. And the non-carcinogenic exposure risk HQ values for children was higher than adult. The HI values of As, Cd, Cr, Cu, Hg, Mn, Ni, Sb, Pb, V and Zn in PM2.5, PM10 and TSP in study area were higher than the human body acceptable limit value (1.0). The non-carcinogenic risk in the study area was relatively serious. Except Co in PM10 and Co, Cr in TSP, which CR values were greater than 10-4, the rest elements CR values were within the acceptable range. Furthermore, CRT values for adult was higher than children in the three aerosol particles. Besides the CRT value (4.78E-05) for children in PM2.5 was less than the acceptable limit (10"4), the other CRT values were all higher than 10"4, which indicated that the carcinogenic risk in study area was serious.4. Migration characteristics of heavy metals in multiple ambient mediumBy analyzing the migration and transformation of heavy metal elements in the soil-rice and surface water-sediment system in the key research area Chang’an Town surrounding electroplating factories, the results show that the difference of absorption and accumulation ability of different heavy metal elements in rice was obvious; Among them, the migration ability of Cd was the highest, Cd migration ability is the strongest, rice is easy to absorb and accumulate Cd from soil, followed by Zn, and the migration ability of Pb was the least; Sediments in the study area of surface water concentration coefficient showed that the sediments easily from surface water absorption enrichment of Cr and Zn, and Cd and Ni migration is weak. In addition, through the analysis of the migration direction of heavy metal elements from water to sediment showed that the heavy metals can easily deposit from water phase to sedimentary phase, but some sampling points exists the phenomenon about the heavy metals release from sedimentary phase to aqueous phase.