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Leaching and aging decrease nickel toxicity to soil microbial processes in soils freshly spiked with nickel chloride.
Koen Oorts1, Uldeen Ghesquiere, Erik Smolders
1Division Soil and Water Management, Katholieke Universiteit Leuven, Faculty of Bioscience Engineering, Kasteelpark Arenberg 20, 3001 Heverlee, Belgium. koen.oorts@hotmail.com
Environmental Toxicology and Chemistry
|June 19, 2007
Summary
Nickel toxicity to soil microbes decreases as the metal ages in soil. Testing nickel toxicity immediately after spiking overestimates its harmful effects, suggesting soils should be leached before toxicity assessments.
Area of Science:
- Environmental Science
- Soil Science
- Ecotoxicology
Background:
- Nickel (Ni) is a trace metal known for long-term immobilization in soils.
- The relationship between decreasing Ni solubility over time and its toxicity to soil organisms is not well understood.
Purpose of the Study:
- To investigate how Ni immobilization and aging in soil affect its toxicity to soil microbial processes.
- To compare Ni toxicity in freshly spiked soils versus aged or leached soils.
Main Methods:
- Three uncontaminated soils with varying pH were contaminated with NiCl2.
- Soils were either experimentally leached or incubated outdoors for up to 15 months.
- Nickel toxicity was assessed by measuring potential nitrification rate, glucose-induced respiration, and C mineralization of maize residue.
Main Results:
- Nickel toxicity, indicated by increased ED50 values (dose inhibiting 50% of a process), was higher in aged soils compared to freshly spiked soils (median factor increase of 4.6).
- Experimental leaching also increased Ni ED50s (median factor of 2.0).
- Toxicity reduction was most pronounced in higher pH soils, correlating with decreased Ni concentration in soil solution.
Conclusions:
- Laboratory toxicity tests on freshly spiked soils overestimate Nickel's toxicity to soil microbial processes.
- Soil aging and leaching reduce Ni bioavailability and toxicity.
- Leaching metal-spiked soils before toxicity testing is recommended to better reflect environmental conditions.
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