Can the sensitivity of soil-dwelling organisms to landfarmed soils contribute to asess the sustainablity of landfarming of oil refinery waste?

Abstract

Beneficial soil organisms inhabiting healthy soils participate in providing soil ecosystem sevices. Oil refineries generate large quantities of solid waste containing several classes of hydrocarbons as well as metals, which are ploughed into the soil during landfarming to utilise the biodegradation capabilities of the ecosystem of the soil. The contaminants may be toxic to these organisms. For the sustainable use of the services of the ecosystem of the soil, it is crucial to know whether remediation had been sufficient for the intended land use. Indicators are needed to assess the degree of recovery. This study aimed to analyse landfarmed soil at an oil refinery chemically and to assess the toxicity and recovery by using a variety of standardised bioassays with the vermicomposting species Eisenia andrei (Oligochaeta) and the springtail Folsomia candida (Collembola). The results showed that soil from the landfarming site, despite remediation, still contained several hazardous chemicals such as diesel range organics, but that the soil mixture was not acutely toxic to the exposed test organisms. It did cause a loss in earthworm (E. andrei) biomass, inhibited cocoon production and also decreased juvenile production of the springtail F. candida. The results suggested the site still needs remediation before landfarming should continue. Bioassays provide a more ecologically relevant assessment of the remediation status of the soil and its toxicity than chemical analysis alone. This finding supports the use of bioassays as an ecotoxicological tool for assessment of landfarmed soils.