Typically, modern WBMs contain fresh or salt water as the base fluid and barite (BaSO4) or ilmenite (FeTiO3) as weighting agent. Clays or organic polymers are incorporated to create a homogenous fluid. Other chemicals (e.g. potassium formate and various glycols) are added to achieve viscosity control, shale stability, cooling and lubrication (c.f. Hudgins, 1994 and Neff, 2005). There is a vast literature on the acute toxicity of WBM components, the presentation of which goes beyond the scope of this review, but in general the acute toxicity of WBM is low (Neff, 1987). Monitoring in the NS (Daan and Mulder, 1993, Olsgard and Gray, 1995, Park et al., 2001 and Renaud et al.,

2008) has not revealed any in situ effects of WBM cuttings on sediment macrofauna community structure, implying that any selleck screening library such effects, if present, will be confined to bottoms inside the innermost stations in these studies, i.e. nearer than 25–250 m from the discharge point. The effects mechanisms of WBM cuttings after sedimentation have been studied in several laboratory and mesocosm experiments. Dow et al. (1990) reported Selleck Sorafenib that redox values were depressed for 3 months in sediments mixed with WBM cuttings in an onshore tank system. Schaanning et al. (2008) exposed undisturbed fjord sediment core samples to thinly sedimented

layers of ilmenite based WBM cuttings. Iron sulphide precipitated under caps thicker than 10 mm. Sediment oxygen (SOC) and nitrate consumption, and release of silicate increased immediately under a 12–46 mm cap. The SOC peaked after 9 days and, for most treatments, returned to background levels after 3 weeks. The increase was positively correlated with cap thickness. A 3 mm cap on top of undisturbed sediment box cores from 200 m depth gave no increase in

SOC, and macrofauna biomass and community structure did not change during a 3 month experiment. In a repeat experiment a 3 mm layer of WBM cuttings caused elevated SOC for more than 3 months and 6–24 mm layers for more than 6 months ( Trannum et al., 2010). After 6 months the macrofauna species richness, abundance, biomass, and diversity were negatively correlated with layer thickness. Corresponding layers with natural sediment did not affect the fauna. Trannum (2011) concluded that the most plausible reason Axenfeld syndrome for the fauna effects was sediment oxygen deficiency due to degradation of organic WBM compounds, presumably mud glycol, although chemical toxicity may have played a role as well. It is not likely that glycol degradation will cause the same effects around a cuttings discharge since the glycol most probably will dissipate before the cuttings reach the bottom. Trannum et al. (2011) found only slight differences in macrofauna recolonization in defaunated trays with coarse and fine sediments capped with 6 and 24 mm ilmenite based WBM cuttings deployed in situ at 200 m depth in the Oslofjord, Norway.