style="font-size:15px;"> Chronic effects of pesticides refer to its long term effects which may require even years to appear. Various body organs such as the lungs, liver, and kidney may be adversely affected due to the chronic impact of pesticides [6]. Reduction in motor signalling and visual ability, as well as impaired coordination and memory, can be attributed to the chronic effects of pesticide exposure [25]. Alteration in levels of human reproductive hormones (male and female) due to prolong presence of pesticide in the body may adversely affect reproductive potential and may result in infertility, stillbirth, birth defects, and spontaneous abortion [29]. Prolong exposure to pesticide may negatively affect the immune system and at the same time may cause various ailments such as hypersensitivity, asthma, and allergies [30]. Furthermore, various negative consequences such as nervousness, dizziness, confusion, nausea, vomiting, tremors, and hypersensitivity toward sound, light, and touch may occur due to ingestion of pesticides such as organochlorines [25].
1.3 Microalgal Species Involved in Bioremediation of Pesticides
Agrochemicals find widespread application in modern day agricultural practices to control pests and weeds to accelerate crop productivity. But environmental deterioration created by these chemicals has compelled human beings to look for an eco-friendly technology such as bioremediation. With the establishment of microalgae as an ideal bioremediation candidate, isolation and selection of strains which are resistant as well as have biodegrading potential received sufficient scientific attention. There are number of scientific investigations which reveal the pesticide degradation capabilities of cyanobacteria and algae (Table 1.2). According to Megharaj et al. [31] cyanobacteria Nostoc linckia, Phormidium tenue, and Synechococcus elongatus and green algae Scenedesmus bijugatus and Chlorella vulgaris had the capability to metabolise two organophosphorus insecticide monocrotophos and quinalphos. They concluded that both cyanobacteria and algae had similar biodegradation potential. In another work Megharaj et al. [32] also showed the biodegradation of the pesticide methyl parathion (MP) by cyanobacteria P. foveolarum, N. muscorum, N. linckia, and Oscillatoria animalis and green algae S. bijugatus and C. vulgaris. The study showed that they were capable of hydrolyzing the insecticide in 20 days while C. vulgaris, N. linckia, and S. bijugatus could hydrolyze the same in 30 days. Thus, it concluded that the biodegradation capabilities of selected microalgal and cyanobacterial strain followed the following order: C. vulgaris < S. bijugatus < N. linckia < N. muscorum < O. animalis < P. foveolarum.
Table 1.2 Cyanobacterial/microalgal strains involved in biodegradation of pesticide.
| Chemical | Microalgae/Cyanobacteria | Reference |
| Monocrotophos and Quinalphos | Chlorella vulgaris, Scenedesmus bijugatus, Synechococcus elongatus, Phormidium tenue, Nostoc linckia | [31] |
| Methyl parathion | C. vulgaris, S. bijugatus, N. linckia, N. muscorum, Oscillatoria animalis, P. foveolarum | [32] |
| DDT | Chlorococcum sp., Anabaena sp., Nostoc sp. | [77] |
| α-Endosulfan | Scenedesmus sp., Chlorococcum sp., | [76] |
| Fenamiphos | Pseudokirchneriella subcapitata, Chlorococcum sp. | [33] |
| Dimethomorph and Pyrimethanil | S. quadricauda | [39] |
| Fluroxypyr | Chlamydomonas reinhardtii | [40] |
| Chlorpyrifos | Synechocystis sp. strain PUPCCC 64 | [41] |
| Prometryne | C. reinhardtii | [43] |
| Anilofos | Synechocystis sp. strain PUPCCC 64 | [42] |
| Acephate, Imidaclorpid | C. mexicana | [44] |
| Diazinon | C. vulgaris | [13] |
| Methyl parathion | Fischerella sp. | [45] |
In addition to this, five green algae (Chlorella sp., Scenedesmus sp. MM1, Stichococcus sp., Scenedesmus sp. MM2, and Chlamydomonas sp.) and five cyanobacteria (Anabaena sp., Nostoc sp. MM1, N. muscorum, Nostoc sp. MM3, and Nostoc sp. MM2) have been reported to degrade fenamiphos which is an organophosphorus pesticide [33].
2,4-dichlorophenol (2,4-DCP) is often used as an intermediate in synthesis of insecticides and herbicides such as 2,4-D. Thus, the release of chlorophenols as industrial waste or by degradation of chlorinated pesticides have cause serious environmental threat [34]. Yang et al. [35] reported biotransformation and enzymatic responses of 2,4-dichlorophenol in Skeletonema costatum (diatom). They demonstrated that Cytochrome P-450, a key enzyme in biotransformation and metabolization, did not play an important role in 2,4-DCP detoxification.
Popular pest control agents such as chlorinated agrochemicals cause serious environmental problems such as accumulation in non-target organisms as well as in water and soil. Considering the high persistence and toxicity of chlorinated pesticide like lindane, many countries have prohibited its direct application [36]. Thus, there is a requirement of potential microalgal strain for eco-friendly remediation of chlorinated pesticides. Kuritz and Wolk [37] evaluated the lindane degrading potential of cyanobacteria N. ellipsosporum and Anabaena sp. genetically manipulated to biodegrade another contaminant 4-chlorobenzoate. Biodegradation of the pesticide lindane by the cyanobacterial strains Synechococcus sp., Oscillatoria sp., Cyanothece sp., Nodularia sp., Synechococcus sp., Nostoc sp., Microcystis aeruginosa, A. cylindrical, M. aeruginosa, A. spiroides, and A. flos-aquae has been reported [38].
Dosnon-Olette [39] demonstrated the removal of fungicides dimethomorph and pyrimethanil and herbicide isoproturon by the microalgae S. quadricauda and S. obliquus. The study showed that S. quadricauda removed dimethomorph and pyrimethanil more effectively than S. obliquus. Fluroxypyr (pesticide) accumulation and degradation by green alga C. reinhardtii was reported by Zhang [40]. They noted that C. reinhardtii had the potential to degrade more than 57% of bioaccumulated fluroxypyr within 5 days.
Singh et al. [41] demonstrated the potential of the cyanobacterium Synechocystis sp.
