Removal of chromium, copper and arsenic from CCA-treated sawdustusing California red worm (Eisenia fetida)

Abstract

In testing for the efficacy of earthworms capability to remove heavy metals from wood protected with chromated copper arsenate (CCA) chemical wood preservative, California red worm Eisenia fetida was exposed to substrate made from a mixture of cow dung and wood sawdust from yellow pine (Pinus sylvesteris) CCA-treated utility pole. The period of exposure of the experiment spanned for twelve weeks. The study was done to ascertain the effects of substrate on the reproduction and total growth development of earthworms Eisenia fetida. Also, the new remediation methodology of using earthworm species to remove heavy metals from CCA-treated wood was tested to determine the amount of heavy metals extracted by Eisenia fetida. The results from ICP-MS analysis at the end of the exposure showed that the percentage removal of CCA heavy metals by earthworms from substrates with respect to the treatment levels and particle sizes of substrate was 52%, 50% and 49% for As, Cr and Cu respectively at treatment level T2 for As and T1 for both Cr and Cu. Arsenic was accumulated from substrate with unsoaked sawdust of 40 mesh while chromium and copper were accumulated from substrate with soaked sawdust of 60 and 40 mesh respectively. The metal bioaccumulation factor (BAF) which showed the inherent amount of heavy metals in tissues of earthworms was evaluated at the end of the experiment. It was revealed that arsenic (As) had the highest bioaccumulated heavy metal in tissues of Eisenia fetida followed by copper (Cu) and chromium (Cr). The population build-up and collective weight gained by earthworms was declined by treatment levels with high amount of CCA-treated sawdust (T3 and T4) as the period of exposure prolonged although substantial growth rate was attained at substrate level T2.