For the treatment of groundwater contaminated with chlorinated hydrocarbons, nano-scaled zero-valent iron (nano Fe0) represents an efficient alternative to other treatments as e.g. pump & treat. Upon selection of a suitable treatment method for a given groundwater a risk-cost-benefit analysis is performed. This analysis does only rarely consider the potential risk of the remediation method for the local environment. However, the assessment of the environmental risk is necessary to avoid a risk-risk trade-off, since any remedial agent may have negative impacts on groundwater ecosystems at the local or regional scale.
In the present study, an environmental risk assessment of the nano Fe0-based remedial agent Carbo-Iron® was performed. Available data for the effects assessment were complemented by studies with the crustacean Daphnia magna, the algae Scenedesmus vacuolatus, larvae of the insect Chironomus riparius and nitrifying soil microorganisms. With these data, a predicted no effect concentration (PNEC) of 0.1 mg/L was determined. Predicted environmental concentrations (PECs) of Carbo-Iron® were derived based on a recent field study. At the point of Carbo-Iron® injection, the PEC of Carbo-Iron® exceeds the PNEC by a factor of 6500. With increasing distance to this point, the risk quotient (PEC/PNEC) decreases and reaches a value of 5 approx. 10 m from the injection point. Beyond this zone, the risk quotient is assumed to be below 1, since migration of Carbo-Iron® in the aquifer is limited.
To determine the suitability of Carbo-Iron® as a remedial agent, a Triad-based approach was developed, integrating the assessment of chemical, physico-chemical and ecotoxicological risks in the groundwater before and after treatment with Carbo-Iron. Based on this assessment, the beneficial influence of the remedial agent of Carbo-Iron® predominated.
For further information, see the publication in Science of the Total Environment:
Weil, M., Mackenzie, K., Foit, K., Kühnel, D., Bundschuh, M., Schulz, R., Duis, K. (2019). Environmental risk or benefit? Comprehensive risk assessment of groundwater treated with nano Fe0-based Carbo-Iron®. Science of the Total Environment 677, 156-166.
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