Abstract
The potworm Enchytraeus albidus has been used as a testorganism to assess the effects of soil polluting chemicals. The current standardized test methods do not exploit the sensitivity of avoidance behavior of the animals towards chemicals as measurement endpoint. In this paper we tested the effect of bauxite residue (BR), the waste from alumina production, on the habitat of a macrodecomposer in three different soils: an acidic sandy soil (NY), a carbonated sandy soil (OB) and a silty soil (NH). In the acute toxicity tests the testing of whole soil samples proved to be more sensitive compared to the testing of soil suspensions and soil extracts, which indicated significant mortality only at over 50 % BR in soil. EC20 values were 9 % BR in OB, 28 % BR in NH and 34 % BR in NY in the whole soil tests of our study. In the avoidance test potworms chose the 1 % and 5 % BR treated soils instead of the control soils, but avoided the 10 % and 25 % BR concentrations. Besides the common methodology applied in avoidance tests, we offered not only control and treated soil pairs to the animals, but we also paired all the concentrations with each other. E. albidus chose 10 % BR amount in soil instead of 25 % BR in all cases. With the avoidance test we could show not only negative, but also positive effects of soil amendments: BR addition to soils at up to 5 % can result in a better habitat for potworms.
Highlights
The potworms or enchytraeids are a group of citellate annelids [1, 2]
In this study we investigated for the first time the avoidance behavior of potworms on bauxite residue amended soils
LC20 values from the acute toxicity tests indicated, that bauxite residue (BR) addition is acceptable for potworms at 9 % in the carbonated sandy soil, at 28 % in the silty soil, and at 34 % in the acidic sandy soil
Summary
The potworms or enchytraeids are a group of citellate annelids (or microannelids) [1, 2]. Potworms have essential role in the decomposition of organic matter and nutrient cycling [3, 4] They have an influence on air permeability, pore structure and aggregate stability in soils [5, 6]. Because of their importance in soil ecosystems, enchytraeids have been used for ecotoxicological testing in laboratory to test the effect of pesticides, metals and other chemicals [7]. Even though each bauxite residue is different in composition, most of them contain Fe2O3, Al2O3, SiO2, TiO2, CaO, Na2O and LOI (loss on ignition) as main components [16] This material is highly saline (> 50 g L-1) and alkaline (pH 10–13), which represents the main disposal problem in the alumina industry [17]. In the standardized method with earthworms and in previous studies with potworms the examined sample was only paired with the control to test avoidance behavior (selection of a preferable area of soil over the area they escape from [2, 12]) [11, 32], but in this study we paired with each other the soil samples amended with various bauxite residue doses to gain a more detailed picture on potworm behavior in contact with bauxite residue amended soils
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