Metabolic responses to subacute toxicity of trace metals in a marine microalga (Thalassiosira weissflogii) measured by calorespirometry

Metabolic responses to the subacute toxicities (non-growth-rate inhibiting) of Cd, Cu, and Zn were measured in the coastal marine diatom Thalassiosira weissflogii using calorespirometry. Respiratory heat production and oxygen consumption rates were measured in diatom cells grown with concentrations of Cd2+ (10(-12) to 10(-8) M), Cu2+ (10(-13.8) to 10(-9.8) M), and Zn2+ (10 (-10.9) to 10(-6.9) M) that are typical of urban and suburban coastal water s. These trace metals did not significantly inhibit diatom growth rates in high-nutrient, high-light laboratory cultures except for the highest concen trations of Cd (Cd2+ = 10(-8) M) and Zn (Zn2+ = 10(-6.9) M). Respiratory he at rates in cells grown with elevated, but non-growth-rate-inhibiting free Cu2+ ion concentrations (10(-11.8) to 10(-9.8) M) were up to 40% higher and oxygen consumption rates were 50 to 75% lower than control ([Cu2+] = 10(-1 3.8) M) cells indicating a subacute depression of respiratory efficiency in Cu-exposed cells. Exposure to elevated free Cd2+ concentrations (10(-10) t o 10(-8) M) caused dramatic short-term (hours) increases (five- to eight-fo ld) in respiratory oxygen consumption rates, which returned to normal in ac climated cells, suggesting a transient disruption of metabolism upon Cd exp osure. Zinc did not significantly affect either respiratory parameter up to a free Zn concentration of 10(-7.9) M, above which diatom growth rate was significantly reduced. The subacute toxic effects of Cd and Cu were more pr onounced in low hin than in Mn-replete cells, consistent with proposed Mn-C d. -Cu antagonisms in marine phytoplankton. The range of free Cu2+ ion conc entrations in coastal waters is similar to that found to cause a decrease i n respiratory efficiency in T. weissflogii, thus coastal marine diatoms may be subject to the subacute metabolic toxicity of Cu. Free Cd2+ concentrati ons in coastal waters are below those found to cause transient subacute str ess in T. weissflogii. Calorespirometry proved to be a sensitive tool for t he assessment of the subacute toxicity of contaminant trace metals.