Phycology and Heavy‐metal Pollution

Abstract

Summary 1. All heavy metals, including those that are essential micronutrients (e.g. copper, zinc, etc.), are toxic to algae at high concentrations. 2. One characteristic feature of heavy‐metal toxicity is the poisoning and inactivation of enzyme systems. Many of the physiological and biochemical processes, viz., photosynthesis, respiration, protein synthesis and chlorophyll synthesis, etc., are severely affected at high metal concentrations. 3. Some algae inhabit waters chronically polluted with heavy‐metal‐laden wastes from mining and smelting operations; Nodularia sp., Oscillatoria sp., Cladophora sp., Hormidium sp., Fucus sp. and Laminaria sp., etc., occur in metal‐rich waters. These algal forms are probably more capable of combating the toxic levels of heavy metals and this attribute is a result of physiological and/or genetic adaptations. The sensitivity or tolerance to heavy metals varies amongst different algae. The phenomena of multiple tolerance and co‐tolerance may be exhibited by some algae. 4. Heavy‐metal pollution causes reduction in species diversity leading to the dominance of a few tolerant algal forms. The primary productivity also decreases after metal supplementation. 5. The uptake and accumulation of heavy metals can be active (energy‐dependent), passive (energy‐independent), or both. 6. Heavy metals can be safely stored as intranuclear complexes by some algae. Notwithstanding this, some changes in the cell wall can enable the algae to tolerate heavy metals by checking the entry of the metals (exclusion mechanism). 7. The metal content of algae growing in a waterbody may yield valuable information for simulating heavy metal pollution: several species of Cladophora and Fucus have been extensively used for this purpose. 8. Several factors affect and determine toxicity of heavy metals to algae. At low pH, the availability of heavy metals to algae is greatly increased, as a consequence of which pronounced toxicity is evident. Hard waters decrease metal toxicity. Some ions, e.g., calcium, magnesium and phosphorus, can alleviate toxicity of metals. 9. The presence of other metals can influence toxicity of a heavy metal through simple additive effect or by synergistic and antagonistic interactions. Similarly, other pollutants can influence heavy‐metal toxicity. 10. The toxicity of heavy metals depends upon their chemical speciation. Various ionic forms of a metal characterized by different valency states, may be differentially toxic to a test alga. 11. Amino acids, organic matter, humic acids, fulvic acid, EDTA, NTA, etc. can complex with heavy metals and render them unavailable. This may eventually lead to less toxicity. 12. Heavy‐metal toxicity largely depends upon algal population density: the denser the population the more numerous the cellular sites available, leading to decreased toxicity.

The removal of uranium from mining waste water using algal/microbial biomass

“…These extracellular polysaccharides also contain ligands which can bind metal ions (Rai et al, 1981). Microbes such as Pseudomonas (Gamma Proteobacteria), and Citrobacter (Omnibacteria) also produce large quantities of extracellular polysaccharides (Liu and Wu, 1993;Marques et al, 1990), which can complex U.…”

Microalgae and Wastewater Treatment

“…Microalgal cultures offer an elegant solution to tertiary and quinary treatments due to the ability of microalgae to use inorganic nitrogen and phosphorus for their growth (Richmond, 1986;Oswald, 1988b,c;Garbisu et al, 1991Garbisu et al, , 1993Tam and Wong, 1995). And also, their capacity to remove heavy metals (Rai et al, 1981), as well as some toxic organic compounds (Redalje et al, 1989), therefore, does not lead to secondary pollution. Amongst beneficial characteristics they produce oxygen, have a disinfecting effect due to increase in pH during photosynthesis (Mara and Pearson, 1986;De la Nou¨e and De Pauw, 1988).…”

“…Microalgal cultures offer an elegant solution to tertiary and quaternary treatments due to the ability of microalgae to use inorganic nitrogen and phosphorous for their growth (Oswald, 1988b,c;Richmond, 1986) and their capacity to remove heavy metals (Rai et al, 1981). Lau et al (1996) studied the ability of Chlorella vulgaris in nutrients removal and reported a nutrient removal efficiency of 86% for inorganic N and 78% for inorganic P. In earlier study, Colak and Kaya (1988) reported an elimination of nitrogen (50.2%) and phosphorus (85.7%) in industrial wastewater treatment and elimination of phosphorus (97.8%) in domestic wastewater treated by algae.…”

Combined toxicity of polycyclic aromatic hydrocarbons and heavy metals to biochemical and antioxidant responses of free and immobilized Selenastrum capricornutum

“…Colby's formula, reviewed by Rai et al [37], was applied to the response data for calculating the expected combined toxicity of the PAH and heavy metal cocontamination. The formula was first derived by Colby in 1967 and reviewed by Rai et al [37] in 1981, based on the assumptions that the chemicals act consecutively on the organism.…”

“…The formula was first derived by Colby in 1967 and reviewed by Rai et al [37] in 1981, based on the assumptions that the chemicals act consecutively on the organism. This formula was used to estimate the type of binary interaction by statistical testing of the null hypothesis of additive toxicity, based on multiplication of the response of the control when exposed to one toxicant and the response of the control when exposed to another toxicant.…”