The effects of new oil-based drill-muds in sediments on the settlement and development of biota in an improved tank test

Previous long-term tank experiments on the effects of oil-based drill-muds in sediments on the settlement and development of biota (Blackman, et al, 1983, Blackman, et al, 1988) are suspected to have suffered from container effects, reducing interstitial water exchange and promoting anaerobiosis. To counteract this, a system has been developed which allows vertical movement of a small proportion of the water entering the tank through the experimental sediments and substrate. An experiment lasting 130 days, with this system showed less evidence of anaerobiosis and confirmed results from previous experiments that there are differences in effect between diesel-based mud and alternative-based muds. A new type of alternative mud formulation, using an oil-in-water emulsion with a much lower base-oil content, was also tested and found to be intermediate in behaviour and effect between the control and conventional muds. To distinguish between toxic effects and those of organic enrichment, the control tank was treated with an artificial drill-mud formulated on medicinal, liquid paraffin. This developed a faunal assemblage different from that in other experimental tanks.