Introduction

Pollution is the addition of pollutant to the environment that causes an adverse effect to the life. There are different types of pollution, but among them, water pollution is an important subgroup. Water is the vital component for life. Surface water and ground water are the major sources of drinking water in rural and urban areas, but due to high industrialization in the recent past decades, the quality has been severely affected (Bharti et al. 2013). Due to industrial revolution, various industries, such as chemical, nuclear, textiles, oil refinery, etc., come in existence, which are a major concern (Persson and Destouni 2009). The problem of water pollution arises due to the release of organic and inorganic pollutants by anthropogenic activity which creates and causes severe health damage (Raouf et al. 2012). Direct disposal of effluents containing pollutants results in the toxicity of surface water bodies and land around industrial areas which leaches down and contaminates ground water bodies to their high density (Prabha et al. 2013). Aquatic system gets to accumulate with high risk of toxins which in turn mixed and transfer into the food chain and finally reaches to humans (Shaikh and Bhosle 2011). After entering into human body, these pollutants cause severe damage to health in terms of renal, cardiovascular, and neurological disorders and are even life threatening (Table 1). It has also been reported that nickel and chromium have a carcinogenic effect on human health (Duruibe et al. 2007).

Table 1 Pollutants causes health damage in humans
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Various physical and chemical methods are used for the detoxification of effluents, but rather than complete degradation, they only change their forms. These changed forms are even toxic and have ability to cause damage even in a very low concentration (Noel and Rajan 2014). Bioremediation over the conventional methods is most promising technology for cleaning environment. In addition, it is an eco-friendly, cost-effective technique having properties for possible recovery of elements and can solve environmental problems related to water (Sahu 2014). The basic protocol of bioremediation and recovery of useful products involve numerous steps, such as selection of biomass (cyanobacterial strain), pre-treatment, immobilization, desorption, etc., as shown in Fig. 1.

Fig. 1
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Schematic representation of biosorption with possible recovery

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Cyanobacteria are aquatic photosynthetic prokaryotes persist more than 3 billion years having unremarkable potential in the treatment of waste water and bioremediation of toxic pollutants from effluents and solutions (Noel and Rajan 2014; Priyadarshani et al. 2011; Rastogi et al. 2014). Recently, there has been an increasing attentiveness about using cyanobacteria as biocontrol agents, either as wild type, mutant or genetically engineered forms (Ananya and Ahmad 2014; Noel and Rajan 2014).

Cyanobacterial bioremediation is based on the idea to take complex pollutants from the environment and use them to boost for their augmentation and metabolism, or renovate them from a toxic to a nontoxic form (Quintana et al. 2011). These cells have high efficiency for binding pollutants, such as toxic metal ions, due to the presence of various lipids, proteins, and polysaccharides receptors on their surface (Priyadarshani et al. 2011). When the toxic complex pollutants are trapped by surface receptors, they bind passively to the cellular structure the phenomena known as “Biosorption”, while the utilization of these pollutants in metabolic cycle after crossing via cell membrane actively is referred to as “Active uptake”. Both passive biosorption and active uptake of pollutants by cyanobacterial cell are termed “Bioaccumulation”, and the phenomenon is referred to as phycoremediation tool (Malik 2004; Sharma 2012). However, the phenomenon can be influenced by various factors, including environmental conditions, contaminants, other microbes, etc., as mentioned in Fig. 2 (Rastogi et al. 2014).

Fig. 2
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Influencing factors for cyanobacterial bioremediation

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Bioremediation of heavy metals

Heavy metals are well-known hazardous pollutants which show a lethal effect on biological cycles of aquatic species due to changes in the conformational configuration of nucleic acids, proteins, and osmotic balance (Sivakumar et al. 2012). The consequence of metal toxicity is not limited to aquatic bodies, but also affects soil flora, plant, animals, and finally to humans. It causes damage to cell morphology and inhibits the cytoplasmic enzyme due to oxidative stress (Bulgariu and Bulgariu 2014). In general, these metals exist naturally either alone or in combination with other elements, but anthropogenic activity enhances their concentration in environment (Ebtesam et al. 2013). Mainly, heavy metals get dissolved in solutions due to their water soluble property, which cause difficulties in their elimination via physical and chemical separation methods. Waste water treatment depends on the precipitation or adsorption of suspended solids, while the use of bio-adsorbent, such as algae, depends on the accumulation of heavy metals (Volesky and Naja 2007). Cyanobacterial approach is an alternative tool for complete removal of heavy metal pollutants with low toxicity due to their cultivate autotrophically and heterotrophically, as well as potential for genetic manipulation (Table 2) (Mitra et al. 2012; Sahu 2014).

Table 2 Heavy metal bioremediation through algae
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In addition to remediation, various studies suggest possible metal recovery from cyanobacterial strains after the treatment of polluted water bodies (Table 3) (Lata et al. 2015).

Table 3 Recovery of metals from waste water through algae
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Bioremediation of oil

Discharge of liquid petroleum contaminant, i.e., crude oil, and their by-products into water bodies due to anthropogenic activities enhance risk in aquatic environment (Almeda et al. 2014). Yearly, 48 % of oil contamination in the oceans is due to fuels and 29 % by crude oil (Brekke and Solberg 2005). Annually, approximately 35 million barrels petroleum has been transport across the world which is an important source of oil contamination (Zaki et al. 2015). In addition, oil refinery discharge is another source which creates pollution in aquatic system (Obaidy and Lami 2014). Oil contamination in rivers and oceans may have effect for short term and long term. Short-term effects include oil toxicity, reduction in dissolved oxygen and light transmission which affects the photosynthetic activity of aquatic organisms. The long-term effect includes a change in the biological process, such as reproduction, food disappearance, and habitat destruction. In addition, it also causes genetic disturbance in aquatic life especially when contaminated with polycyclic aromatic hydrocarbons (PAH) (McGenity et al. 2012).

PAH is originated by incomplete fuel combustion or petroleum derivatives spill out (Dabestani and lvanov 1999). These are highly toxic pollutants which show mutagenic and carcinogenic effect when comes in contact with life either by the means of direct contact or via food chain (Perelo 2010). PAH degradation by the conventional methods is not very easy, as they accumulate in the sediment due to their high molecular weight, low water solubility, and hydrophobicity (Hong et al. 2015). Hence, there is an urgent need for appropriate management to solve such problems and to develop technologies which are more effective and resource conservative. Various studies demonstrate unremarkable potential of algal remediation for removing crude oil and their toxic by-products (Table 4) (Houser et al. 2014; Olajire and Essien 2014). From crude oil, 38–60 % saturated hydrocarbon and 12–41 % aromatic hydrocarbon degraded using cyanobacteria, while 10–23 % of aliphatic hydrocarbon and 10–26 % aromatic compound from motor oil (Priyadarshani et al. 2011).

Table 4 Degradation of petroleum compounds and fuel components by algae
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Bioremediation of pesticides

Pesticides are the toxic chemicals which are specifically used in fields for removing pests including insects, weeds, pathogenic fungi, rodents, etc (Rani and Dhania 2014). However, excessive use may results in the aggregation of these chemicals in agricultural product, soil, surface water, as well as ground water (Mohany et al. 2011). The phenomena of aggregation may result in geno and cytotoxicity, dysfunctioning of immune system, reduction of reproductive health, and even mortality (Gibbons et al. 2015). In addition, it may also enhance risks to ecosystem and affect a wide range of soil and water microflora. Invertebrates, such as earth worm, which are essential for soil processes, are found to be more sensitive for sublethal and lethal effects of these insecticides (Chagnon et al. 2015). Harmful compounds, such as organochlorine and organophosphorus, are introduced into an aquatic system by agriculture run-off (Karunya and Saranraj 2014).

The rate of degradation process depends on selected algal strain and nature of pesticide which can be influenced by environmental conductions (pH, salinity, oxygen tension, nutrients, water, temperature, light intensity, etc.) and physicochemical properties (molecular weight, concentration, chemical structure, toxicity, etc.), respectively (Varsha et al. 2011; Priyadarshani et al. 2011) (Table 5).

Table 5 Microalgae in the bioaccumulation of pesticides
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Bioremediation of radioactive compounds

In our environment, radioactive compounds have been released from several decays by various anthropogenic activities. Unlike industrial effluent, radionuclide comes into surroundings from metallurgical mining, nuclear power test, discharge from nuclear reactors, etc. The toxicity of radioactive compound is furthermost environmental anxiety which poses a major concern for health issue and is serious threat for life. Various studies revealed a lethal effect on human health due to direct contact, including the risk of leukaemia, leucopenia, kidney damage, and even genetic disorders (Prakash et al. 2013). While indirect transmission of this toxic radionuclide via food chain also causes serious health hazards. After release, these compounds get suspended in the atmosphere for long time in the form of radioactive dust. This contaminated dust gets settled by the phenomenon of radioactive fallout and causes pollution in soil and surface water bodies which finally gets transmitted to food web (Groudev et al. 2001).

Among all radionuclides, Uranium isotopes (238U, 235U, and 234U) consider as most dangerous element due to its high toxicity and radioactivity (Newsome et al. 2014). Continuous mining and refining of uranium release many tons of radioactive pollutants which increase the risk of air, water, and soil contaminations. Individual can be exposed to uranium by inhalation, ingestion, and dermal contact. Soluble form of concentrated uranium when ingest shows chemotoxic effect to renal tissue which ultimately leads to the failure of kidney (Gavrilescu et al. 2009). In addition, zirconium (89Zr, 95Zr, 93Zr, and 88Zr) and thorium (232Th, 230Th, and 229Th) are other hazardous radioactive nuclides which show risk of cancer and lungs toxicity in humans. These pollutants also have capability to store in bone tissues and make a significant change in genetic material even after delay exposure (Humsa and Srivastava 2015).

Various studies suggest the potential of algal cells for the removal of radioactive pollutants from waste and its importance for the maintenance of sustainable environment (Table 6). Live or dead cells of Synechocystis sp. can remediate uranyl ion due to the presence of an extracellular hemolysin, such as protein (HLP), which conjugate with polysaccharides and help in the adsorption of radioactive compound (Kalin et al. 2004; Fukuda et al. 2013).

Table 6 Algae in the bioremediation of Radionuclides
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Conclusion

Nowadays, environmental pollution is a major concern in front of mankind. Due to rapid industrialisation and other anthropogenic activities, the level of various pollutants is increasing in nature which finally enhances the risk of human health. Domestic and industrial effluents, radioactive and pesticide wastes, oil, and their by-products, etc are the main source of pollutants, which contain toxic complex compounds. For safe and sustainable environment, there is an urgent need to enhance awareness about the source of pollutants and to develop an effective methodology for remediation with their real applications. However, the conventional techniques are used often, but they can only transform their form; therefore, the next generation water treatment techniques are in high demand. Algal bioremediation is an eco-friendly, cost-effective, precisely sensible technique for resolving the environment problems. However, further research needs to focus on the mechanism behind the remediation on genetic and molecular levels to finally facilitate their exploitation.