The Development of Risk-based Remediation Target Value for Lead Contaminated Soils

With the rapid economic development, China is experiencing increased land contamination and lead poisoning problem in recent years, which is no longer restricted to isolated incidents and locations. There is an urgent need to remediate the lead contaminated soils to protect the public’s health. However, contaminated land remediation and determination of remediation target value has been neglected for years. In order to accommodate uncertainties within the conservative point estimation of remediation target value for lead contaminated soils, Monte Carlo simulation technique is integrated into the traditional calculation model from a probabilistic perspective. Risk-based remediation target values for lead contaminated soils of different land use types (including school/hospital, residential, business and industrial use) are developed preliminarily. Furthermore, this study highlights the necessity to determine the remediation target value on the basis of actual (i.e. site-specific) risks to humans and, besides, actual risks due to contaminant migration. Introduction Lead persists in the environment in lead paint, old plumbing and contaminated soil. And lead poisoning is an environmental and public health hazard on a global scale [1]. The health effects of lead exposure include developmental neurotoxicity, reproductive dysfunction and toxicity to the kidneys, endocrine and blood systems [2, 3]. Children are more vulnerable to lead poisoning than adults because they breathe air closer to the ground, where lead concentrates, and they also are more likely to put lead-contaminated objects in their mouths [4]. It has been demonstrated that blood lead (PbB) levels of 10-15 micrograms/dL in newborn and very young infants result in cognitive and behavioral deficits [5]. In China, due to large-scale production, consumption and lack of regulations, lead is emitted into the environment in large quantities through wastewater irrigation, solid waste disposal and sludge application. As a result, lead is present in the environment continuously [6], especially in soil, which could act as a reservoir for lead pollution over the years. Previous studies have founded serious lead pollution in soil in the vicinity of mining and smelting factory [7, 8], electronic waste recycling site [9], lead-acid battery factory [10] and coal-fired power plant [11]. Since 2005, health related incidents caused by lead pollution in soil have raised sharply in China, which occurred in Fengxiang County in Shanxi Province, Dafeng County in Jiangsu Province, Jiyuan County in Henan Province and Heyuan County in Guangdong Province. Moreover, it is suggested that children's BLLs in China are higher than those of their counterparts in other countries due to its heavy lead pollution [12]. Public concern is growing over the accumulation of lead in soil. Therefore, remediation of lead contaminated soils is of great public health importance. Over the past decade, soil contamination has emerged as a key environmental issue, not only in China, but worldwide. The development of remediation programs has evolved rapidly, and almost all have been initiated during the 1980s [13]. One of the first published sets of generic guidelines was the "Multimedia Environmental Goals" developed for the USEPA in the 1970s. However, the values were based largely on professional judgment. In these years, remediation guidelines have been produced by considering routes of exposure, effects on human health, effects on human use of the land, and influence on the rest of the environment. These soil guidelines specify one or more threshold concentrations, which if exceeded, indicate the possibility of adverse effects occurring [14]. Quantitative risk assessments have been conducted at more than 70% of the US Superfund sites [13]. In the framework of the Dutch Soil Protection Act, Target and Intervention Value have been developed based on potential risks to humans and ecosystems in Netherlands [15]. To date, little research on remediation target value for contaminated soils in China has been conducted. Guidelines for Risk Assessment of Contaminated Sites (draft for discussing) just propose a procedure to determine the remediation target value for contaminated soils based on conservative point estimation of health risk. However, risk assessment is becoming increasingly complex. There are many sources of variation, including quantification of potential exposure pathways, choice of calculation model and parameter values, definition of the level of "acceptable" risk, and variation in the way the overall method is applied. Neglecting such uncertainties may result in missing information and, thus, impractical decision support with regard to soil remediation. The aim of this study is: 1) to propose a procedure to determine the remediation target value for contaminated soils by integrating risk assessment model and Monte Carlo simulation technologies. 2) to develop the risk-based remediation target value for different use types of lead contaminated soils from a probabilistic perspective. Materials and Methods Model of Remediation Target Value Calculation. Exposure varies depending on an individual’s lifestyle. As to heavy metal contaminated soils, ingestion and dermal contact of soil contribute to the overall daily intake of heavy metal contaminants mainly [7]. Exposure analysis is the process of estimating the intensity, frequency and duration of human exposures to an agent currently present in the environment or of the estimating hypothetical exposure that may arise from the release of new chemicals into the environment [16]. The equation for calculating the contaminant intake dose through ingestion is as follows: AT BW ED EF SIR C CDII     