Assessing the combination of iron sulfate and organic materials as amendment for an arsenic and copper contaminated soil. A chemical and ecotoxicological approach

• The combination of iron sulfate and organic materials efficiently reduced As solubility.
• Organic matter did not interfere with iron oxides capacity to immobilize As.
• Cu mobility was more influenced by pH than by organic matter addition.
• Combining iron sulfate and compost provides a good alternative for the whole remediation process.

The efficiency of combining iron sulfate and organic amendments (paper mill sludge, olive mill waste compost and olive tree pruning biochar) for the remediation of an As- and Cu-contaminated soil was evaluated. Changes in As and Cu fractionation and solubility due to the application of the amendments was explored by leachate analysis, single and sequential extractions. Also, the effects on Arrhenatherum elatius growth, germination of Lactuca sativa and toxicity to the bacteria Vibrio fischeri were assessed. The combination of iron sulfate and the organic amendments efficiently reduced As solubility and availability through the formation of amorphous iron oxides, while organic matter did not seem to mobilize As. At the same time, copper fractionation was strongly affected by soil pH and organic matter addition. The soil pH significantly influenced both As and Cu mobility. Within all the amendments tested, FeSO4 in combination with compost showed to be the most suitable treatment for the overall remediation process, as it reduced As and Cu availability andenhanced soil nutrient concentrations and plant growth. In sipte of contradictory trends between chemical analyses and ecotoxicity tests, we can still conclude that the application of organic amendments in combination with reactive iron salts is a suitable approach for the remediation of soils contaminated by Cu and As.