Toxicity of Drilling-Mud Biocides to Developing Estuarine Macrobenthic Communities

The effects of various blocides, as used in drilling muds for exploratory drilling for oil offshore, were determined by comparing macrobenthic communities that developed from planktonic larvae in treated and untreated aquaria. Surflo®-B33 and Aldacide® were tested simultaneously. Harvest at seven weeks yielded 1,941 animals, representing 37 species of 6 phyla. The etfects of Surflo-B33 (25% dichlorophenol and other chlorophenals) on these communities were similar to those of pentachlorophenol (Tagatz et al, 1977; 1978), a biocide known to be toxic to many aquatic organisms (Rao, 1978). Significantly fewer (a=0.05) chordates, mollusks, and annelids occurred in 819 µg Surflo-B33/l (measured) than in the control; mollusks were most sensitive and also significantly fewer in aquaria receiving 41 µg/l. Average numbers of animals and species per aquarium did not significantly decrease in Aldacide (91% paraformaldehyde) at nominal concentrations of 15 and 300 µg/l. The high toxicity of the chlorophenols tested indicates that use of alternative biocides, possibly paraformaldehyde, should be considered for natural waters

Effects of a Lignosulfonate-Type Drilling Mud on Development of Experimental Estuarine Macrobenthic Communities

Drilling mud, as used in exploratory drilling for oil offshore, affected the composition of estuarine communities that developed from planktonic larvae in aquaria containing sand and flowing estuarine water. Aquaria contained: sand only; a mixture (by volume) of 1 part mud and 10 parts sand; 1 part mud and 5 parts sand; or sand covered by 0.2 CIU mud. For all environments, annelids, mollusks, arthropods, and coelenterates were the numerically dominant phyla collected in a 1 mm mesh sieve after eift weeks exposure; a total of 1,025 animals, representing 45 species, was collected. Annelids and coelenterates were significantly fewer (a=0.05) in aquaria containing drilling mud than in the control aquaria. Arthropods were significantly affected only by mud cover over sand; mollusks also were diminished in this environment, but not significantly. Exposure to concentrations of drilling mud reduced not only the number of individuals, but also the frequency of occurrence of macrobenthic species. Thus, the average number of annelid species in 1 part mud: 5 parts sand aquaria or in mud-covered aquaria was significantly less than in control aquaria, The average number of arthropod species per aquarium was also significantly less in the mud-cover exposure than in the control. Discharge of large quantities of drilling mud at levels tested in the laboratory could adversely affect the colonization of various substrata by benthic animals in nature