Aquatic Toxicity Testing of Various Freshwater Drilling Additives

The leading suppliers of drilling fluid solutions in the industrial drilling markets have begun to focus on the environmental impact of their products throughout their life cycle, from production and packaging to use and disposal.  In the first phase of responsible stewardship, companies focused on the down-hole activity of their products, primarily using the ANSI/NSF Standard 60 Drinking Water Treatment Chemicals protocol as the benchmark for responsible use.  Today, interest is focused on the effect of drilling fluid products in the environment. Fluid additives for the non-oilfield drilling markets commonly consist of the industrial mineral bentonite, natural cellulosic material and derivatives (PAC), and commonly accepted water treatment polymers such as partially hydrolyzed polyacrylamides (PHPA).   These fluid systems routinely achieve certification to ANSI Standard 60 and are generally regarded as the best available fluid technologies for drilling water wells, horizontal directional bores, mineral exploration wells, and geothermal heat loop drilling and grouting.  The U.S. Fish and Wildlife Service, administered by the U.S. EPA, offers the opportunity to assess the toxicity of products potentially introduced to the various aquatic habitats   Specifically, common drilling fluid products can be tested on two freshwater species designated by the USFWS, these species being the Daphnia pulex (a freshwater copepod) and Pimephales promelas (fathead minnow).  Tests on these species generate LC₅₀ and NOEC data which determine the lethal concentration with a 50 percent survival rate and the no observable effect concentration of the exposed species.  Using the USFWS Rating Scale, products fall in a range between relatively harmless and super toxic. The data generated through USEPA-accepted toxicity testing can aid government regulatory agencies, as well as the end user of drilling fluid products, in assessing the environmentally responsible use of drilling fluid products.