Abstract
In this study, we reported on the responses of three Malaysian green algae, Caulerpa racemosa, Caulerpa lentillifera and Ulva reticulata against three heavy metals, copper (Cu), lead (Pb) and mercury (Hg). Responses were determined as maximum quantum yield (Fv/Fm) for photosynthetic quantum efficiency, chlorophyll (chl) a content and relative growth measured as changes in fresh weight. The algae were exposed for 8h in two concentrations of metals, which were 1 mg/L and 2 mg/L. In general, all algae were severely affected by the presence of Hg compared to the other two metals. Fv/Fm of the algae was significantly reduced to the lowest of 18% in 1 mg/L Hg as observed in C. racemosa while the lowest for Cu and Pb was 29% and 41%, respectively, also observed in similar algal species. All algae showed an undetected value of Fv/Fm when concentration of Hg was increased to 2 mg/L. An increase in Fv/Fm was observed for C. lentillifera in 1 mg/L of Cu and Pb but the value showed a reduction when the concentration of both metals was increased to 2 mg/L. Among the algae, Fv/Fm of C. racemosa was severely affected by the presence of all metals particularly at 2 mg/L where it showed undetected value. An increase in the content of chl a was observed in C. racemosa and C. lentillifera for each metals at both concentrations while a decrease in the content was observed in U. reticulata. Algal relative growth was negatively affected by the presence of metals with Hg showed the strongest effect. However, some algae showed a positive effect of Pb on their growth.
Highlights
One of the worldwide pollution concerns is the water contamination by heavy metal ions due to their possible toxic effects on aquaticorganisms
All the algae were greatly affected by the presence of Hg with 82% Fv/Fm reduction in C. racemosa, 47% reduction in C. lentillifera and 13% reduction in U. reticulata at 1 mg/L (Figure 1.0a)
Fv/Fm of C. racemosa was severely affected by all metals at 2 mg/L.At the physiological level, the measurement of Fv/Fm is an effective parameter to assess the photosynthetic status the photosystem II (PSII) of the alga under stress in which a reduction in this parameter indicates that the alga has been exposed to stress [17]
Summary
One of the worldwide pollution concerns is the water contamination by heavy metal ions due to their possible toxic effects on aquaticorganisms. Industries contributed the most for the discharge wastes that lead to this environmental problem include mining and smelting of metalliferous compounds, surface finishing industry, energy and fuel production, fertilizer and pesticide industry, and electroplating [1]. These discharges can contaminate the marine ecosystems which are among the largest of the aquatic ecosystems. High levels of Hg in the form of Hg2+, for example, have strong phytotoxic effects and when present in toxic concentrations can induce visible injuries and physiological disorders in cells triggering the production of reactive oxygen species (ROS) leading to cellular disruption [9]
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