Toxicity of Cadmium to Caenorhabditis Elegans (Nematoda) in Whole Sediment and Pore Water—the Ambiguous Role of Organic Matter

Abstract

A bioassay using the nematode Caenorhabditis elegans was performed with natural sediment that had been spiked with organic matter (36-117 g total organic carbon/kg dry wt) and cadmium (Cd; 10-1,200 mg/kg wet wt). Whole sediment and pore water were tested to study the influence of particulate organic matter (POM) and dissolved organic matter (DOM) on Cd toxicity and to compare the toxicity of the two sediment phases. Toxicity was measured with nematode growth as test parameter. No toxicity was observed if sediment concentrations of Cd were below concentrations of acid-volatile sulfides (AVS). At higher Cd concentrations, toxicity in whole sediment and pore water increased with increasing organic content. This phenomenon was explained by an increase of DOM concentrations in organically enriched treatments and a resulting solubilization of Cd due to Cd complexation by DOM. Because DOM did not alter the bioavailability of Cd for the nematodes, bacteria, serving as food, might have functioned as vectors for Cd-DOM complexes, so that Cd could have become available in the gut of the nematodes. A higher toxicity in whole sediment compared to in pore water in the organically enriched treatments indicated that POM-bound Cd may have contributed to the toxicity of Cd to C. elegans.

The Effect of Sediment Type and pH-Adjustment on the Porewater Chemistry of Copper- and Zinc-Spiked Sediments

“…Sediment-porewater partition coefficients in their study were in the range of 1 × 10 3 -1 × 10 5 L kg −1 for Zn spike concentration of 650 to 2500 µg g −1 , the higher K d range being a product of greater concentrations of AVS, a strong metal binding phase. For metal-spiked oxic/sub-oxic (non-sulfidic) sediments, K d values are commonly <10 3 L kg −1 due to poor equilibration and pH effects (Green et al, 1993;De Witt et al, 1996;Leonard et al, 1999;Hoss et al, 2001;Besser et al, 2003;Milani et al, 2003).…”

“…Extended periods of equilibration between the sediment and water (porewater, overlying water) are required before the partitioning of the added metal, Fe or Mn begin to resemble that occurring in natural sediments with similar metal concentrations (Lee et al, 2004;Simpson et al, 2004;Burton et al, 2006a;Zhong and Wang, 2006;Hutchins et al, 2007). Despite the often poor resemblance to naturally contaminated sediments, metal-spiked sediments are frequently used for toxicity assays to assess species sensitivity to metals (Green et al, 1993;De Witt et al, 1996;Leonard et al, 1999;Hoss et al, 2001;Besser et al, 2003;Milani et al, 2003).…”

Conducting Ecological Risk Assessments of Inorganic Metals and Metalloids: Current Status

“…Thus metal-accumulation tends to be both organism-and situation-specific. Höss et al (2001) noted that nematodes living in sediments may incur toxicity from Cd despite the metal being bound by the dissolved organic matter (DOM) in the pore water. They hypothesized that bacteria, serving as food for the nematodes, might have functioned as vectors, or the nematodes might have ingested Cd bound to organic matter directly.…”

Discovering Capacity in Novel Targets: C. Elegans as a Model Life Form in Toxicological Research

“…The underlying strategy created by Donkin and Dusenbery [315][316][317][318][319][320][321][322][323][324][325][326][327][328] has prompted to an institutionalized soil toxicological testing technique received in 2001 by the American Society for Testing and Materials and as of late the International Standards Organization in Europe (ISO 2007). The underlying extraction technique has been enhanced using transgenic strains of nematodes which takes into consideration GFP-named worms to be utilized that recognizes the worms being tried in soils from the vast quantities of indigenous species that are comparable in size and appearance.…”