A simple model of possible copper contents in earthworms using model soil extracts from old vineyards; a comparative assessment of NH₄NO₃ and CaCl₂ extracts

Abstract

Copper contents assessed in an NH₄NO₃ extract and CaCl₂ extract were determined to evaluate their impact on soil fertility using earthworms as indicators of sustainable agriculture and the maintenance of biological diversity. The final evaluation can be conducted when the field surveys on the earthworm coenose have been com­pleted.

So far, the surveys have covered the earthworm coenoses of 15 vineyards. The obtained data were used in a simplified approach to find out whether it is possible to perform a risk assessment on available copper in model extracts for the pathway soil/soil organisms in soils under organic or conventional management. The small sample size (n = 49) does not allow for a final evaluation at present. It is, however, possible to see tendencies.

The area values evidenced a high correlation of R² ~ 0.79 between the copper content in the NH₄NO₃ extract and the quotient of total content in soil organisms divided by the content in the soil extract (bioconcentration factor – BCF) of the earthworm coenose. However, the correlation of earthworm-available copper in the CaCl₂ extract with the BCFs of the earthworm coenose calculated for each area resulted only in a mean coefficient of R² ~ 0.52.

The use of BCFs has the advantage that all factors responsible for the availability of copper at a given site are reflected by the actual copper contents in an earthworm coenose and are included in the model through the extract contents.

The results obtained so far support the use of the NH₄NO₃ extract as an appropriate model to predict copper contents in earthworm coenoses of vineyards with long-term treatment. The exposure data collected from field surveys and the percentage of mobile copper can be subjected to simple regression analysis to perform a first assessment of the risk potential of copper in the pathway soil/soil coenose and accumulation in the earthworm coenose.

When the total content does not exceed ~ 300 mg Cu kg^–1 soil (TM), copper was found to accumulate in lumbricidae only to a limited amount. This indicates the adaption of soil organisms to site conditions.

The modeling of possible copper contents in soil quality indicators requires further surveys of earthworm coenose further evaluate which extraction procedure is appro­priate to determine the copper content in organisms suitable for risk assessment.