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

Abstract

AbstractMetabolic responses to the subacute toxicities(non‐growth‐rate inhib iting)ofCd, Cu, and Znweremeasured 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+ (10−138 to 10−98 M), and Zn2+ (10−109 to 10−6.9 M) that are typical of urban and suburban coastal waters. These trace metals did not significantly inhibit diatom growth rates in high‐nutrient, high‐light laboratory cultures except for the highest concentrations of Cd (Cd2+ = 10−8 M) and Zn (Zn2+ = 10−6.9 M). Respiratory heat 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+] = 10−13.8 M) cells indicating a subacute depression of respiratory efficiency in Cu‐exposed cells. Exposure to elevated free Cd2+ concentrations (10−10 to 10−8 M) caused dramatic short‐term (hours) increases (five‐ to eight‐fold) in respiratory oxygen consumption rates, which returned to normal in acclimated cells, suggesting a transient disruption of metabolism upon Cd exposure. 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 pronounced in low Mn than in Mn‐replete cells, consistent with proposed Mn‐Cd, ‐Cu antagonisms in marine phytoplankton. The range of free Cu2+ ion concentrations in coastal waters is similar to that found to cause a decrease in respiratory efficiency in T. weissflogii, thus coastal marine diatoms may be subject to the subacute metabolic toxicity of Cu. Free Cd2+ concentrations in coastal waters are below those found to cause transient subacute stress in T. weissflogii. Calorespirometry proved to be a sensitive tool for the assessment of the subacute toxicity of contaminant trace metals.