Drilling mud-evoked hydranth shedding in the hydroid Tubularia crocea

At 100 000 ppm, the suspended particulate and liquid phases of a reference drilling mud and a used production mud significantly increase the hydranth shedding proportion in the hydroid coelenterate Tubularia crocea after 48 h. At 10 000 ppm only the liquid phase of the synthetic drilling mud significantly increased hydranth shedding. At 1000 ppm the 3% iron and calcium forms of the five lignosulphonates tested were found to be toxic. Other organic constituents of drilling muds found to be toxic included, tannic acid (100 ppm), paraformaldehyde (1 ppb), and water-soluble fractions of crude oil and No. 2 fuel oil (approximately 20 ppm). Mercury, cadmium, copper, cobalt, zinc and nickel were found toxic at 100 ppm. Exposure to 0.1?0.001 ppm mercury, 1% WSF of crude oil, and 10 ppm cadmium resulted in a significant decrease in the hydranth shedding proportion. This reduction in hydranth shedding proportion may reflect hormesis, a stimulation of growth by low-level exposure to a pollutant, but cannot be conclusively demonstrated until growth measurements are made.