Metal accumulation in the green macroalga Ulva fasciata: effects of nitrate, ammonium and phosphate.

Coastal organisms are often exposed to both metal pollution and nutrient enrichment. The influences of major nutrients (nitrate, ammonium, and phosphate) on the accumulation of trace metals (Cd, Cr, Zn and Se) in Ulva fasciata were examined. The relative accumulation of metals was quantified by the kinetic measurements of accumulated metal concentration over a short exposure period (8 h). Our study demonstrated that macronutrients could markedly influence the rate of metal accumulation in the macroalgae. An increase in ambient nitrate concentration resulted in a significant increase in Cd accumulation rate, whereas the rate of accumulation of Cr and Zn was not greatly affected by the ambient nitrate level (between 10 and 100 microM). Zn uptake in nitrate-enriched macroalgae was, however, significantly higher than its uptake in N-starved macroalgae. The accumulation of Cd, Cr and Zn was not appreciably affected by the concentration of ammonium. Se accumulation was significantly inversely related to the ambient phosphate concentration, presumably due to the competitive inhibition by a high P concentration. Cr accumulation in the macroalgae increased significantly with increasing phosphate concentration. These data implied that the influences of major nutrients on cationic and anionic metal accumulation were highly metal-specific. The dependence of metal accumulation on major nutrients will appreciably affect our prediction of metal accumulation in macroalgae and the interpretation of biomonitoring data using the Ulva species.