How are earthworms affected by lead contaminated soil from shooting ranges?

FFI-Report 2020

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20/01623

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978-82-464-3273-1

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1.9 MB

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Jorunn Aaneby Ida Vaa Johnsen
Earthworms are important for a number of soil functions, but earthworms can be adversely affected by lead (Pb) and other contaminants in the soil. Soils in shooting ranges may contain high concentrations of Pb and other metals originating from ammunition. The bioavailability of Pb in ammunition residues is not necessarily comparable to the bioavailability of more soluble Pb salts which are often used in risk assessments. Soil properties such as pH, content of total organic carbon (TOC) and cation exchange capacity (CEC) can affect earthworms and the bioavailability of Pb in soil. This study investigated the influence of Pb on earthworms in soils with different properties. Survival, growth, reproduction and uptake of Pb in earthworms (Eisenia fetida) in soil from five shooting ranges in different parts of Norway was investigated. Clean and contaminated soil from each shooting range was mixed to obtain different concentrations of Pb. The earthworms showed a high degree (>7 of 10) of survival in all the soils, both in the samples of clean soil and in the soil mixtures with concentrations of Pb up to 3300 mg/kg. Variations in the growth and reproduction of the earthworms in the clean soil samples from the different shooting ranges indicated that the soil properties affected the earthworms. The growth of the earthworms seemed to be affected by Pb in the soil from some of the shooting ranges, while Pb significantly affected the reproduction of the earthworms in the soil from all the shooting ranges. The number of juveniles in the soil mixtures decreased with increasing concentration of Pb, and no significant reproduction was detected in soil with >500 mg Pb/kg. The uptake of Pb in the earthworms increased with the concentration of Pb in the soil mixture that the earthworms had been exposed to, but the uptake was also affected by the soil properties. Statistical analyses indicated that TOC and CEC of the soil had a negative effect on the growth and reproduction of the earthworms, while pH had a positive effect. The TOC and CEC of the soils were strongly correlated, and these parameters were negatively correlated with the soil pH. The correlations made it difficult to determine which parameter(s) that had the greatest impact on the growth and reproduction of the earthworms. Earthworms which had been exposed to soil with approximately 1500 mg Pb/kg for four weeks were transferred to clean soil. After the transfer, the earthworms could reproduce, even if they had not excreted accumulated Pb. The results indicated that high concentration of Pb in the soil did not damage the reproductive function of the earthworms, but the juveniles did not tolerate high concentration of Pb and did not survive in the contaminated soil. A risk assessment based on the results showed that to protect (95%) both the earthworms and the animals that eat earthworms, the concentration of Pb in the soil should not exceed natural background concentration. The reproduction results showed that the earthworms did not reproduce in soil with high concentrations of Pb, and if the earthworms do not stay in soils with high concentration of Pb, the risk of secondary poisoning can be considered small.

About publication

Report number

20/01623

ISBN

978-82-464-3273-1

Format

PDF-document

Size

1.9 MB

Download publication

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