Leaching impacts Ni toxicity differently among soils but increases its predictability according to nitrification assay

Abstract

Purpose Deriving toxicity thresholds through bioassays has become the scientific basis for the risk assessment of metal contamination in soils, but few studies have been reported for Ni toxicity in Chinese soils. In addition, although leaching has been recommended to increase the ecological relevance of the output of soil toxicity bioassays, its impacts on Ni threshold and soil solutions in soils remained to be shown. Therefore, in this study, 17 soils were collected throughout China and were assessed for Ni toxicity using substrate-induced nitrification (SIN) assay for both un-leached and leached treatments. Meanwhile, soil solutions of all Ni treatments were extracted and analyzed. This study provides information for the development of a terrestrial biotic ligand model (TBLM) for Ni in Chinese soils.Materials and methods Soils were artificially amended with NiCl 2 solution to generate nominal Ni contamination levels, and aliquot of each Ni treatment was leached with artificial rain to prepare leached soil samples. All the 17 unleached and the 17 leached soils were subjected to the standard SIN protocol. A total of 816 microcosm tubes were established. Soil solution was extracted, and the solution physiochemical properties were analyzed for each Ni treatments. Both the total-Ni-based and the solution-Nibased median effective concentrations (EC50) in unleached soils and leached soils were calculated from dose-response curves. Free-Ni 2+ -based EC50 was also calculated based on solution chemical properties. Leaching effect was assessed based on these results. Results and discussion Ni EC50 varied largely among soils for both the total-Ni-based and the solution-Ni-based EC50 in un-leached soils. In un-leached soils, the total-Ni-based EC50 values ranged from 52.8 mg kg −1 (Hulunber soil) to 2,385.4 mg kg −1 (Wulumuqi soil), and the solution-Nibased EC50 ranged from 0.70 mg L −1 (Jiaxing soil) to 293.35 mg L −1 (Wulumuqi soil). Stepwise multiple regressions showed that soil pH and total Ca were the best predictors for the total-Ni-based EC50. Protective effects of Ca 2+ and Mg 2+ but not H + against Ni toxicity in soil solution were found. Leaching impacted Ni EC50 differently among soils, with leaching factor ranging from 0.2 (Haikou soil) to 19.7 (Hulunber soil) for the total-Ni-based EC50 and from 0.1 (Dezhou soil) to 35.7 (Jiaxing soil) for the solution-Ni-based EC50. In addition, predictability of Ni EC50 was higher in leached soils. The variations in Ni EC50 were in agreement with the findings in previous studies. Soil pH and Ca may play important roles in the partition of Ni in Chinese soils and thus impact the Ni toxicity. Protective effects of Ca 2+ and Mg 2+ in soil solutions against Ni toxicity may exist, but the role of H +

Lead toxicity thresholds in 17 Chinese soils based on substrate-induced nitrification assay

“…The results agreed with a previous report that Ni toxicity to barley root elongation was significantly decreased by leaching in an alkaline soil (pH ≥ 8.2) (Li et al, 2011). However, in contrast to recent studies (Li et al, 2009;Schwertfeger, 2011), we found a significant decrease in Pb toxicity with leaching for one acidic soil (Nanning (pH 4.34)) and three neutral soils (Jiaxing (pH 6.67), Jingzhou (pH 6.74) and Harbin (pH 7.26)). This effect can be explained by the impact of leaching on the composition of the soil solution (Li et al, 2010;Oorts et al, 2007).…”

“…All leached and unleached soils were used to establish a standard SIN assay (Li et al, 2009(Li et al, , 2010Oorts et al, 2006b). Three replicates of 7 g amended soil for each Pb treatment were preincubated under dark aerobic conditions at 20 ± 2°C in 50-mL centrifuge tubes.…”

“…PNR values were calculated from the linear increase in soil nitrate plus nitrite after ammonium addition (Li et al, 2009(Li et al, , 2010Oorts et al, 2006b). PNR data were fitted to a log-log doseresponse curve (Haanstra et al, 1985) in Microsoft Excel (Eq.…”

“…Bradham et al (2006) concluded that soil pH was the most important factor related to Pb bioavailability and toxicity to earthworms. Although it is widely recognized that soil properties play a crucial role in affecting toxicity (Cremazy et al, 2013;Li et al, 2011;Li et al, 2009Li et al, , 2010Oorts et al, 2006bOorts et al, , 2007Rooney et al, 2006Rooney et al, , 2007, few countries have incorporated soil physicochemical properties in their soil quality guidelines. With scientific data like that provided by the present studies, the ecologically relevant Chinese soil guidelines could improve more quickly.…”

Uptake and toxicity of spiked nickel to earthworm Eisenia fetida in a range of Chinese soils

“…However, a lack of ecotoxicological data for metals in Chinese soils is still one of the critical factors that preclude the development of Eco-SSVs in China [15]. Recently, a few studies have been conducted to investigate the variations of Ni toxicity to plants and microbial processes (nitrification) in a range of Chinese soils [6,7], but none has investigated the toxicity of Ni to soil invertebrates.…”