A novel method for investigation of uptake and distribution of polluting microelements and nanoparticles in soil-inhabiting nematodes

Nematodes are key components of soil ecosystems and important bioindicators. The effect of soil contamination on soil biota may be studied very well with nematodes due to their small size, semipermeable cuticle and complex life processes. The uptake of three elements (copper, chromium and zinc) was studied by means of electron probe microanalysis (EPMA) and focused ion beam (FIB) technique. Adult females of the plant-feeding nematode, Xiphinema vuittenezi were investigated. The animals were treated with 1 mmol/dm3 Cu(NO3)2 or CuSO4; 50 mmol/dm3 K2CrO4 solutions and 50 mg/dm3 nano-ZnO suspension. Following the treatment, nematodes were rinsed, plunged into liquid nitrogen for 2 min in order to carry out quick-freezing and lyophilized for 72 h. The stylet and cuticle were studied in case of the CuSO4 treated worm by EPMA. In the cuticle, the distribution of copper and sulfur showed high correlation. In the stylet and the lip surrounding the stylet, much more sulfur was found, than elsewhere, while the copper intensity was higher than the average just in the lip region. In case of nematodes treated with Cu(NO3)2 or K2CrO4 solutions or ZnO suspension, focused ion beam technique was applied in order to prepare cross-sections. One-dimensional distribution of the treating elements, furthermore phosphorus and sulfur was studied. In all cases the treating elements (Cu, Cr, Zn) and the above-mentioned two essential microelements showed a similar pattern: decreasing intensity toward the center of the cross-section. Consequently, the main element uptake route is the cuticle and not the gut. The correlations between the treating elements and phosphorus as well as sulfur (high correlation for Cr and P; Cr and S; Cu and S; moderate correlation for all other combinations) suggest the role of these elements in toxicant binding and detoxification.