Cadmium, the most toxic heavy metal, has no biological function, and significant potential for adverse human health effects. Previous studies explored the utility of the macro-alga Chara australis for bio-remediation of cadmium-contaminated sediments. This study assesses the bio-remediation potential of the close relative, and salt tolerant species, Chara longifolia, through a series of four questions. First, how does cadmium in the soil impact survival and biomass production? Second, how much cadmium does C. longifolia accumulate in plant tissues? Third, does C. longifolia concentrate cadmium in its tissues relative to the concentration in the soil? Lastly, where is the cadmium localized within the plant cell? These questions are assessed for sediment cadmium concentrations of 0 ppm, 25 ppm, and 35 ppm, in freshwater and saltwater. Using a euryhaline species such as C. longifolia, and assessing fresh and saltwater contexts, is important because many cadmium-contaminated sites are old mining and smelting areas, associated with acidic and saline wastes. Methodologically, a standard set of growth measurements were taken at the beginning and end of the experiments, inductively coupled plasma mass spectrometry was used to assess cadmium uptake and accumulation, and dithizone staining followed by light microscopy was used to visualize cadmium localization.
Results/Conclusions
Initial experiments showed a minimum cadmium-contamination-survival of at least 20 days, with all cadmium-exposed saltwater C. longifolia surviving for at least 39 days, while the first freshwater specimen death occurred on day 21. Some cadmium-exposed specimens exhibited greater longevity, with 17% of cadmium-exposed freshwater plants alive on day 30 and 27% of cadmium-exposed saltwater plants alive on day 70. Assessment of cadmium uptake in saltwater C. longifolia via inductively coupled plasma mass spectrometry revealed a statistically significant increase in cadmium uptake between experimental and control conditions, (0.08 ppm to 11 ppm cadmium) but lower overall cadmium accumulation than C. australis. This experiment also didn’t show statistically significant changes in growth with cadmium exposure. A semi-quantitative cadmium visualization approach revealed cadmium dithizone precipitates near cell walls and chloroplasts in C. longifolia. Based on the data, saltwater C longifolia has some bio-remediation potential, but is not a hyper-accumulator of cadmium. Qualitative observations throughout the experiments revealed that the fresh and saltwater systems may behave differently, and ongoing research is assessing the cadmium bio-accumulation dynamics of freshwater C. longifolia. Based on aqueous chemistry, we expect greater bio-remediation potential through greater cadmium uptake in the freshwater incubation.