Assessment of heavy metals mobility and toxicity in contaminated sediments by sequential extraction and a battery of bioassays

Abstract

The aim of this study was to assess heavy metals mobility and toxicity in sediments collected from a dam reservoir in the conditions of intensive human impact by using chemical fractionation and a battery of bioassays. In the studies, the test organisms were exposed to substances dissolved in water (Microtox, Phytotestkit) as well to substances absorbed on the surface of solid particles (Phytotoxkit, Ostracodtoxkit F). The studies showed that sediments from the Rybnik reservoir are toxic, but the tested organisms showed different sensitivity to heavy metals occurring in the bottom sediments. The sediment samples were classified as toxic and very toxic. Moreover, the studies showed a higher toxicity in solid phases and whole sediment than in pore water. The lowest sensitivity was observed in H. incongruens (solid phases) and V. fischeri (pore water, whole sediment). The studies revealed that the toxicity of the sediments is caused mainly by heavy metal forms associated with the solid phase of the sediments. The studies did not confirm the metals occurring in fraction I (exchangeable) to be bioavailable and toxic to living organisms because most correlations between the metal concentration in fraction I and the response of the organisms were negative. The highest mobility from the bottom sediments was found in zinc, average mobility—in copper, cadmium and nickel, and low mobility—in chromium and lead. Organic matter is likely to be the most important factor controlling metal distribution and mobility in the studied sediments.

The application of the germination index in the assessment of the phytotoxicity of bottom sediments from the Rybnik Reservoir

“…For each of the plants, the mean value of the germination index indicated the dominance of the inhibitory effect of the tested sediment on plant growth. Baran & Tarnawski (2015) who reported that S. saccharatum is the most sensitive species for identifying phytotoxic sediment samples compared to L. sativum and S. alba. Among dicotyledonous plants, S. alba turned out to be a more sensitive one since up to 73% of the sediment samples were observed to inhibit its growth.…”

“…Low or no toxicity of sediments from heavy metals may be caused i.a. by their presence in a very stable and insoluble form, a high content of organic matter or clay fraction as well as a neutral or a slightly alkaline reaction (Baran & Tarnawski 2013, 2015. The studies conducted by Gong et al (2001) and Czerniawska-Kusza et al (2006) also confirmed that the false assessment may be caused by sediments rich in organic matter, which can hide the inhibitory effect of pollutants on test plants.…”

“…The area around the reservoir is characterised by great diversity, from recreational development with dispersed urban development, through numerous industrial and commercial areas, dumping grounds and heaps, up to a small number of areas used for agriculture and forestry. The reservoir constitutes a part of the technological chain of Elektrownia Rybnik S.A. as a direct receiver of industrial and rainwater sewage, sewage from a water treatment plant, blowdowns from cooling towers, and as an essential source of cooling water (Baran & Tarnawski 2015, Baran et al 2016). There is a strong emission of dust and gas pollution in the Silesian Voivodeship, accounting for 19% of the total emissions in Poland.…”

“…In the study of Baran et al (2017), it was found that individual PAHs, such a NAP, PHE, FLT, PYR, BAA, CHR, BAP, in sediments from the Rybnik Reservoir indicated a higher possibility of the occurrence of an adverse ecological effect. In addition, the specific interactions occurring between pollutants may also result in antagonistic or synergistic effects, the prediction of which may be challenging (Kabata-Pendias & Pendias 1999, Baran & Tarnawski 2015, Czarniewska-Kusza et al 2006, Simeonov et al 2007.…”

Assessment of metal leachability and toxicity from sediment potentially stored on land

“…The occurrence of metals in sediments is extremely important from an ecological point of view, because some metals are toxic (Pb, Cd, Hg), and all in excess are harmful to living organisms (Baran and Tarnawski, 2013;. An important feature which distinguishes metals from other undesirable substances is the fact that they do not undergo biodegradation but only biotransformation (Singh et al, 2005;Yuvanatemiya and Boyd, 2006;Rabajczyk, 2011;Baran and Tarnawski, 2015). Metals may be immobilized in the sediments for a long time, but in variable atmospheric conditions they may be easily leached from the sediments and pose a hazard of returning the element to cycling in nature (Rabajczyk, 2011;Baran et al, 2011;Baran and Tarnawski, 2013).…”