Source apportionment and risk assessment of heavy metals in urban soils from a central China city by using positive matrix factorization model coupled with Monte Carlo simulation

Abstract

Urban soils are an integral ingredient of the urban ecosystem, and whether heavy metals do harm to the city inhabitant health has been brought to the forefront. A total of 78 urban soil samples were collected from Zhengzhou, and the contamination level, source apportionment, concentration-oriented and sourceoriented risk evaluation of pollution elements in the samples were carried out in the study. Results showed that Cd was the most serious contaminant and constituted considerable ecological risk compared to other elements. Four Factors (natural source, industrial production, agricultural activities and traffic discharges) were distinguished through the positive matrix factorization model in conjunction with correlation analysis, and their respective contribution rates were 18.73%, 33.22%, 23.91% and 24.14%. The probability distribution of health risk assessed by means of Monte Carlo simulation revealed that noncarcinogenic risks associated with heavy metals were acceptable for both adults and children, while the total carcinogenic risk values remained relatively high. Moreover, the children were more susceptible to health risks in comparison to adults, and the ingestion way was considered to be the major exposure pathway. The results of source-oriented health risk demonstrated that the agricultural source was the major contributor to health risks, which was characterized by As, Ni and Co.

Exposure Factors in Health Risk Assessment of Heavy Metal(loid)s in Soil and Sediment

“…For the following parameters, point values were usually used: exposure duration (ED), particulate emission factor (PEF), skin surface area (SA), dermal absorption factor (ABF), average time (AT), the conversion factor (CF), lifetime (LT), reference dose (RfD), and cancer slope factor (CSF). The concentrations for most analyzed HMs had a lognormal distribution [5,59,65,78,84,117,121,[128][129][130][131], while the normal distribution for some elements was used in several articles [84,121,131]. Most researchers used a triangular distribution for the ingestion rate (IngR) of adults and children [5,37,59,65,117,121,128,[130][131][132][133][134], but a lognormal distribution was also used in a significant number of articles [12,63,64,78,84,135,136], especially for the ingestion rate of children [12,63,64,78,84,[134][135][136][137].…”

“…The concentrations for most analyzed HMs had a lognormal distribution [5,59,65,78,84,117,121,[128][129][130][131], while the normal distribution for some elements was used in several articles [84,121,131]. Most researchers used a triangular distribution for the ingestion rate (IngR) of adults and children [5,37,59,65,117,121,128,[130][131][132][133][134], but a lognormal distribution was also used in a significant number of articles [12,63,64,78,84,135,136], especially for the ingestion rate of children [12,63,64,78,84,[134][135][136][137]. In some works, a normal distribution was also used as the type of probability distribution [129], or point values were applied [18].…”

“…In some works, a normal distribution was also used as the type of probability distribution [129], or point values were applied [18]. For the InhR, a lognormal distribution [37,61,64,84,117,128,136] or point values [18,121,130,131,134] were used in the calculation of probabilistic health risk assessment, where the use of the lognormal distribution was more prevalent both for adults and children. A triangular distribution was mainly used for EF [12,18,37,63,65,84,117,[128][129][130][131][133][134][135][136][137]; however, in some articles, point values [59,78,121,132] or a uniform distribution [64] was also applied.…”

“…For the InhR, a lognormal distribution [37,61,64,84,117,128,136] or point values [18,121,130,131,134] were used in the calculation of probabilistic health risk assessment, where the use of the lognormal distribution was more prevalent both for adults and children. A triangular distribution was mainly used for EF [12,18,37,63,65,84,117,[128][129][130][131][133][134][135][136][137]; however, in some articles, point values [59,78,121,132] or a uniform distribution [64] was also applied. Point values were usually used for ED, at 24 years for adults and 6 years for children [18,37,59,117,[130][131][132]134].…”

“…A triangular distribution was mainly used for EF [12,18,37,63,65,84,117,[128][129][130][131][133][134][135][136][137]; however, in some articles, point values [59,78,121,132] or a uniform distribution [64] was also applied. Point values were usually used for ED, at 24 years for adults and 6 years for children [18,37,59,117,[130][131][132]134]. Several researchers stated other values, such as 70 years for adults [78,133,137] and 18 years [133,137] or 10 years [78] for children, as well as a different number of years depending on the element [129].…”