Use of Ulva lactuca to distinguish pH-dependent toxicants in marine watersand sediments

Ulva lactuca (sea lettuce) is a cosmopolitan marine attached green seaweed capable of sequestering high environmental levels of ammonia. Ammonia can b e acutely toxic to marine organisms and is often found in dredged sediments from highly industrial areas or from areas with high carbon inputs. For th e purposes of dredged sediment disposal as well as in determining causes of toxicity in complex mixtures, it is important to distinguish ammonia toxic ity from the toxicity of other compounds. The use of U. lactuca to selectiv ely remove ammonia from waters and sediments as part of a toxicity identifi cation and evaluation (TIE) procedure was evaluated. Ulva lactuca lowered c oncentrations of total ammonia from 75 to 17 mg/L in <8 h in water-only exp osures. This treatment also reduced 48-h amphipod mortality from 75 to 20%. In whole sediments, U. lactuca lowered interstitial water concentrations o f ammonia from 60 to 20 mg/L, while keeping overlying water concentrations below detectable limits (<1 mg/L). To determine the limitations of the U. l actuca method to selectively remove ammonia from solution, metal and organi c accumulation experiments were performed. Ulva lactuca generally took up < 15% of metals present, with most of the exposures resulting in less than a 10% uptake. In contrast, U. lactuca removed 77% of lindane and 95% of fluor anthene. Results of a TIE conducted on sediments from an industrial marine harbor indicated U. lactuca was useful, in conjunction with other procedure s, in categorizing ammonia as a sediment toxicant.