We determined the toxicity of oil refinery waste in three soils using the springtail Folsomia candida (Collembola) in bioassays. Sublethal exposure to a concentration series of API-sludge presented EC50's for reproduction of 210 mg/kg in site soil; 880 mg/kg in LUFA2.2- and 3260 mg/kg in OECD-soil. The sludge was the least toxic in the OECD-soil with the highest clay and organic matter content, the highest maximum water holding capacity, and the least amount of sand. It was the most toxic in the reference site soil with the lowest organic matter content and highest sand content. The results emphasized the important role of soil characteristics such as texture and organic matter content in influencing toxicity, possibly by affecting bioavailability of toxicants.
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.
Landfarming is used in southern Africa as a tool to dispose of contaminants in the petrochemical industry. A historically landfarmed site was identified at a petroleum refinery where the sludge deposited on the site consisted of a mixture of oil and water-soluble contaminants which included several hazardous chemicals. The aim of this study was to assess the toxicity of the sludge, as well as of soil from the landfarming site, and to determine if potworms and plants could be used in bioassays since there is a need to identify a variety of test species, representing different ecological niches. We exposed a soil-dwelling potworm (Enchytraeus doerjesi) to the sludge and the landfarming soil to study their survival, growth, reproduction success and avoidance behaviour. Five plant species and their seeds were exposed to different concentrations of sludge in potting soil, and consequently germination success, growth rate and biomass were monitored. The various soils from the landfarming site were not acutely toxic to the potworms and they even showed an increase in reproduction, compared to uncontaminated control soil. They avoided heavily contaminated soil from the landfarming site. We conclude that the potworms were not as sensitive as the earthworms and springtails previously tested. They may nevertheless still be utilised for testing the toxicity and recovery status of such soils, since they represent a different ecological niche and showed an avoidance response to refinery waste. The plants were not very sensitive to refinery sludge and presented mixed results. Lettuce and grass were affected most by the sludge, while beans were the most resistant. With the addition of low concentrations of sludge to the substrate, the growth rate of beans was even stimulated.
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