Ecotoxicological effects of brine discharge on marine community by seawater desalination

To determine ecotoxicological effects of brine discharge from the desalination plant and the potential tolerance impact associated with various marine communities, marine ecotoxicological assessment was carried out using four phytoplankton species (Skeletonema coastatum, Chlorella vulgaris, Tetraselmis suecica and Isochrysis galbana) and macroalgae (Ulva pertusa) as primary producer, and two zooplankton species (neonate for rotifer Brachinonus plicatilis, adult of harpacticoid copepod Tigriopus japonicus) and one demersal fish (olive flounder, Paralichthys olivaceus) as consumers. Values of 72 h EC50 of population growth inhibition (PGI) for S. costatum, C. vulgaris, T. suecica and I. galbana were estimated as 55.1, 61.7, 56.9 and 42.2 ppt, respectively, and I. galbana was the most sensitive to brine. No significant differences in brine sensitivity were found in the ranges of 30.0-45.0 ppt for S. costatum and T. suecica, and less than 40.0 ppt for I. galbana. Mortality rates of B. plicatilis neonate and adult of T. japonicus revealed that brine less than 60.0 ppt caused <50% mortality and over 65.0 ppt showed >50% mortality for the two species in terms of acute toxicity. 24 h LC50 and LOEC value of rotifer neonate (68.1 ppt and 55.0 ppt, respectively) were higher than those of T. japonicus (63.6 ppt and 40.0 ppt, respectively) for 96 h test periods. Spoluration rate of green algae U. pertusa sharply decreased from 60.0 ppt and 0% between 65.0 and 80.0 ppt with a 96 h EC50 value of 53.3 ppt. Survival of olive flounder fry P. olivaceus significantly decreased with the increase of brine concentration and the 96 h LC50 value was estimated as 48.6 ppt, lower than green algae, but NOEC (40.0 ppt) of olive flounder was not different from that of green algae. In general, 40 ppt of salinity seems to be a threshold concentration for acute toxicity of brine. Differences of brine effect on each test species has a connection with difference of eco-physiological characteristics such as tolerance of organism on brine, exposure times, and natural habitats of test species. Therefore, site-specific test strategy is highly recommendable to reflect the local ecosystems for the brine discharge and also site selection of desalination plants.