Enhanced Uptake of Arsenic Induces Increased Toxicity with Cadmium at Non-Toxic Concentrations on Caenorhabditis elegans

Abstract

Cadmium (Cd) and arsenic (As) are widely distributed pollutants that co-exist in the environment; however, their joint toxicity on living organisms is still largely unknown. In this study, we explored the joint toxicity of concurrent exposure to Cd and different As species at low concentrations on Caenorhabditis elegans (C. elegans) in comparison to single exposures. Endpoints such as germ cell apoptosis, the number of oocytes, brood size, and the life span were employed to evaluate the combined effects of Cd and As on exposed C. elegans from L3 or L4 stages. Our results showed that concurrent exposure to non-toxic concentrations of Cd and As caused the synergy of reproductive and developmental toxicity. The presence of Cd promoted the accumulation of As in both germline and intestine detected by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Although a conversion of As(III) to As(V) was detected as dependent on pH according to the microenvironment of the intestine in the worm, there was no significant difference of toxicity in C. elegans concurrently exposed to Cd and different As species. Using loss-of-function mutant strains, As was deemed responsible for the enhanced joint toxicity, and in which gcs-1 played a key protective role. These data help to better evaluate the comprehensive adverse effects of concurrent exposure of heavy metals at low concentrations on living organisms in the environment.

Keywords: C. elegans; arsenic species; bioaccumulation; cadmium; joint toxicity.

Figure 1

Images of AO stained apoptotic cells in the gonads (A,B) and the determination of non-toxic concentrations of (C) Cd, (D) As(III), and (E) As(V) based on germ cell apoptosis. * Means p < 0.05.

Figure 2

Effects of single and co-exposure to non-toxic concentrations of Cd, As(III), and As(V) on (A) germ cell apoptosis, (B) brood size, and (C) the number of oocytes. * Means p < 0.05.

Figure 3

Effects of single and co-exposure to non-toxic concentrations of Cd, As(III), and As(V) on (A) average life span and (B) survival rate. * Means p < 0.05.

Figure 4

Spatial distribution of Cd and As in C. elegans exposed to Cd, As(V), and Cd-As(V).

Figure 5

Changes of As species corresponding to different pH. (A) As(III) and As(V) trends, (B) As(III) and As(V) contents.

Figure 6

The effect of single and co-exposed Cd, As(III), and As(V) on apoptosis gonad cells of strains mtl-2 (gk125) and gcs-1 (ok436). * Means compared with the corresponding groups of N2, p < 0.05.