Toxicological review of the possible effects associated with inhalation and dermal exposure to drilling fluids production streams

Drilling fluids are used extensively in the upstream oil and gas industry and are complex mixtures comprising of solids and liquids, including base oils and brine. The fluid has many roles during the drilling process including removing cuttings, cooling and lubricating the drill bit and carrying various chemicals down the borehole. The fluid is cleaned by passing over a shale shaker, where unwanted solids are removed and theresultant cleaned fluid is then re-injected into the well. Drilling fluid compositions can broadly be divided into oil-based and water-based fluids, but show a wide range of composition within each of these categories. Othersubstances that may be present in oil-based systems include inorganic salts, emulsifers, titanium dioxide, crystalline silica, thickeners, surfactants, small quantitiesof strong bases such as lime, sodium hydroxide or potassium hydroxide. The waterbased systems show an even wider variability in composition. They typically contain metal salts and may contain natural thickeners (e.g. bentonite) or artificial thickeners(e.g. polyethylene glycol), barium sulphate and other mineral phases. They may also contain preservatives and biocides such as glutaraldehyde. Workers can be exposed to drilling fluids by inhalation and skin contact.The aims of the toxicological review were to update an earlier review by Eide (1990) ofthe health effects associated with inhalation exposure to vapour and aerosol generatedfrom oil-based drilling fluids and to evaluate the potential effects dermal exposure towater and oil-based drilling fluids. Our review took into account the concentration ofindividual components in fluids and the potential influence of different components indetermining the toxicity of the mixture, although there are very few data that describehow the toxicity of individual substances may be modified by the presence of othersubstances in a mixture.The main/This report and all IOM’s research