Use of a general toxicity test to predict heavy metal concentrations in residential soils C. Marjorie Aelion a,b, * , Harley T. Davis a a Department of Environmental Health Sciences, Room 401, University of South Carolina, 921 Assembly Street, Columbia, SC 29208, USA b Marine Science Program, University of South Carolina, Columbia, SC 29208, USA Received 4 May 2006; received in revised form 1 September 2006; accepted 18 October 2006 Available online 30 November 2006 Abstract Significant clusters of developmental delay and mental retardation (DD/MR) were identified in children born in South Carolina. Although it is difficult to identify one factor that causes DD/MR, environmental insult including exposure of pregnant women to heavy metals can induce DD/MR in their children. Because it is expensive to measure the concentrations of individual metals in large numbers of environmental samples, the general Microtox Ò toxicity test was used to identify highly toxic soil samples. Approximately 100 soil sam- ples were collected from residential areas and analyzed to determine an effective concentration (EC 50 ) of soil required to inhibit 50% light emission of the luminescent bacterial test organism (Vibrio fischeri). The EC 50 values were then transformed to relative toxicity units (RTU). A subset of 56 high and low toxicity soil samples was then analyzed by inductively coupled plasma–atomic emission spectrometry (EPA method 6010) for arsenic, lead, and chromium, which are known neurotoxins. The highest measured arsenic concentration was 30 times higher than the South Carolina residential soil limit. Significant correlations were found between the RTU and soil arsenic and chromium concentrations. Microtox Ò also identified some low arsenic and chromium samples as toxic, presumably because additional unidentified toxicants were present in the soil. In general, however, the Microtox Ò test was effective in identifying soils with elevated concentrations of arsenic and chromium, even in residential neighborhoods where limited soil toxicity was expected. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Microtox Ò ; Arsenic; Chromium; Residential soil contamination 1. Introduction Humans are responsible for the release of large quanti- ties of metals, including arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), and mercury (Hg) into the envi- ronment (Nriagu and Pacyna, 1988). Once released, these metals are cycled between environmental media. Soils may become highly contaminated due to both direct land disposal of wastes and fallout from atmospheric emissions. Heavy metals in particular have long residence times in soils because of sorption to soil particles (Fetter, 1992), which increases the potential risks for human exposure and adverse human health effects, at both the cellular level (Delmas et al., 2000; Fulladosa et al., 2002) as well as higher levels (Stewart et al., 2003). Metal exposure to humans has been widely studied. Dif- ferent populations show disproportionate susceptibilities to metals (Vahter et al., 2002). Infants and children are partic- ularly susceptible to neurotoxicological damage from metal exposure due to their ongoing rapid intellectual develop- ment. The neurological systems of fetuses, often the target of damage from metals, are also at risk because of the transfer of maternal blood in which metals may bioaccu- mulate (Caldero ´n et al., 2003). Arsenic, chromium, and lead are three metals of partic- ular concern for neurological impairment. A strong associ- ation was found between lower intelligence scores in 0045-6535/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2006.10.042 * Corresponding author. Address: Department of Environmental Health Sciences, Room 401, University of South Carolina, 921 Assembly Street, Columbia, SC 29208, USA. Tel.: +1 803 777 6994; fax: +1 803 777 3391. E-mail address: aelionm@sc.edu (C. Marjorie Aelion). www.elsevier.com/locate/chemosphere Chemosphere 67 (2007) 1043–1049