Effect of soil properties on lead bioavailability and toxicity to earthworms

Abstract

Soil properties are important factors modifying metal bioavailability to ecological receptors. Twenty-one soils with a wide range of soil properties (USA; http://soils.usda.gov/technical/classification/taxonomy/) were amended with a single concentration of Pb (2,000 mg/kg) to determine the effects of soil properties on Pb bioavailability and toxicity to earthworms. Earthworm mortality ranged from 0 to 100% acute mortality following exposure to the same total concentration of Pb (2,000 mg/kg) in amended field soils. Internal Pb concentrations in earthworms ranged from 28.7 to 782 mg/kg, with a mean of 271 mg/kg. Path analysis was used to partition correlations in an attempt to discern the relative contribution of each soil property. Results of path analysis indicated that pH was the most important soil property affecting earthworm mortality (p < 0.01) and internal Pb (p < 0.05). Soil pH was related inversely to mortality and internal Pb, soil solution Pb, and Pb bioavailability. The most important soil property modifying reproduction was amorphous iron and aluminum oxides (FEAL). Because FEAL is rich in pH-dependent cation-exchange sites, several soil properties, including pH, FEAL, and cation-exchange capacity, have a causal effect on Pb adsorption and soluble Pb. Path analysis is useful for assessing contaminated soils with a wide range of soil properties and can assist in ecological risk assessment and remediation decisions for contaminated sites. Soil properties are important factors modifying metal bioavailability and toxicity and should be considered during the ecological risk assessment of metals in contaminated soils.

Determining the bioavailability and toxicity of lead contamination to earthworms requires using a combination of physicochemical and biological methods

“…In the present study, the effect of pH was weaker for internal Pb than for reproduction (Table 3). This was not in agreement with the results observed by Peijnenburg et al (1999), Langdon et al (2005) and Bradham et al (2006). Internal Pb concentrations did not correlate with soil OM content, but they significantly and negatively correlated with DOC level in the porewater.…”

“…The significant correlation between earthworm survival and pH most likely is caused by the direct effect of (low) soil pH on earthworm survival (Spurgeon and Hopkin, 1996). Bradham et al (2006) argued that the apparent correlation of earthworm survival with CEC may be caused by the strong inter-correlation between CEC and other exogenous variables such as pH, and not by a direct effect of CEC (see e.g., Criel et al, 2008). Earthworm mortality was not significantly correlated with organic matter content or DOC concentration in the porewater, which agrees with other studies (Bradham et al, 2006;Janssen et al, 1997;Peijnenburg et al, 1999).…”

“…2C). The correlation between reproduction and CEC was highly significant (Bradham et al, 2006), but CEC is directly related to soil pH (Sauvé, 2002;Bradham et al, 2006). In addition, Ca, Cd and Zn concentrations and silt content significantly and positively affected juvenile numbers, while a high sand content seemed to reduce juvenile numbers.…”

“…Bradham et al (2006) argued that the apparent correlation of earthworm survival with CEC may be caused by the strong inter-correlation between CEC and other exogenous variables such as pH, and not by a direct effect of CEC (see e.g., Criel et al, 2008). Earthworm mortality was not significantly correlated with organic matter content or DOC concentration in the porewater, which agrees with other studies (Bradham et al, 2006;Janssen et al, 1997;Peijnenburg et al, 1999). Simple and stepwise regression analysis showed that the number of surviving of adult earthworms (SN) was well predicted on the basis of the porewater Pb concentrations, CEC, silt and sand contents of the test soils (Table 4).…”

“…Grelle and Descamps (1998) also found that soil total Pb concentration was a better predictor of earthworm body burden than CaCl 2 -extractable Pb levels. Previous studies demonstrated that soil physicochemical properties have a significant impact on Pb uptake by E. andrei (Spurgeon and Hopkin, 1995;Peijnenburg et al, 1999;Bradham et al, 2006;Smith et al, 2012). For example, soil pH has been suggested as the most important factor for controlling the bioavailability of Pb in soil, followed by organic matter content (Thomas, 1997;Peijnenburg et al, 1999).…”