The effect of treated drill cuttings on benthic recruitment and community stucture-an experimental study on a natural seabed

Abstract

Environmental effects of treated cuttings were experimentally in situ. The cuttings orginated from drilling with a low toxicity oil based mud. The base oil and aromatic content in the orginal test materiale were 0-20% and 0-285 µg/g respectively. Environmental effects were tested by 1) faunal changes after the addition of a 3 mm layer of cuttings on a natural benthic community, and 2) recolonization of a azonic sediment mixed with 10 % cutting. Treatments with cutting with a high baseoil content (15-20%) resulted in severe effects. Significant but less severe effects could also be seen in cuttings treated with a baseoil content of 2-3%. Tests with standard thermal treated (200-250°C) cuttings (baseoil content 0.3%) gave no significant effects. The solvent washed (hexane) cuttings (baseoil content 1.45%) resulted in few environmental effects. Some effects could, however, be seen on the three species of polychaetes. Based on the total species matrix for the experiment on a natural benthic community, the threshold for gross effects on community structure was a sediment base oil concentration of 1000 ppm. Some individual species showed effects at a base oil content between 150 and 1000 ppm.