Bioconcentration, bioaccumulation and biomagnification of pesticide
The presence of pesticide residues in soil/water and then ill/adverse effects on various organisms have drawn global attention. These man-made plant protection chemicals, namely, organochlorines like dichlorodiphenyltrichloroethaue (DDT) along with its metabolites like (dichlorodiphenyldichloroethaue [DDD] and dichlorodiphenyldichloroethylene [DDE]), hexachlorocyclohexaue (HCH), benzene liexachloride (BHC), cyclodienes like—aldrin and dieldrin, toxapliene and polychlorinatedbiphenyls (PCBs) have been reported to be bioaccumulative and bio-toxic (Mostafalou and Abdollahi 2013, Robinson et al. 2015). Nine organoclilorine pesticides, namely, DDT with DDE and DDD. HCB, aldrin, dieldrin, eudrin, heptachlor, chlordane, toxapliene, and mirex, have been identified as persistent organic pollutants (POPs) in the 12th Stockholm Convention due to their prolonged persistence, wide distribution across various environmental components (soil, air, and water), lipophilic nature and ability to accumulate in various trophic levels, resulting in higher accumulation in higher levels of the food chain and are also toxic to animals and humans. Indiscriminate and non-judicious use of these pesticides has resulted in the worldwide presence of their residue, even in Arctic areas (Garbariuo et al. 2002). These are the result of bioconceutration, bioaccumulation, and biomagnifications of toxic residues of pesticides. Bioconcentration is known as the concentration of a contaminant taken up by the aquatic organisms, provided that water is the only source of contaminant. The bioconcentration factor (BCF) is calculated as the concentration of pesticide residue in biota and water. Bioconcentration of a pesticide residue is controlled by 3 factors, namely, (i) physico-chemical property of the pesticide molecule, (ii) condition of the aquatic organism, and (iii) environmental condition. Physico-chemical properties include, mainly, water solubility (WS), octanol/water partition coefficient (K0„.) and molecular size. The BCF can be expressed as follows:
Pesticides with low WS and higher Koxv and bigger molecular size (diameter < 15 A0) have higher BCF (Dimitrov et al. 2002). Among the physiological conditions of aquatic organisms, parameters like size, biochemical constituents (mainly lipid), and metabolism will change with the growth stage of the organism, which will certainly result in variations in uptake, elimination, and bioconcentration profiles (Swackhamer and Skoglund 1993). The environmental condition including pH, salinity, temperature of water, and quantity of dissolved/adsorbed organic matter significantly affects the bioconcentration. Bioconcentration of chlorinated pesticides has been reported to increase with an increase in temperature for various species of fishes, algae, mussels, etc. (Nawaz and Kirk 1995, Fisher et al. 1999). Now, bioaccumulatiou means the intake of contaminants from both food dietary sources and water. Factors responsible for bioaccumulation include dissolved/particulate organic carbon in water, namre of button sediments, and physiological condition of aquatic organisms. Further, biomaguifications combine both processes of bioconcentration and bioaccumulation resulting in an increase in contaminants’ concentration at higher trophic levels. Dining the trophic transfer of pesticide residues, the trophic transfer coefficient (TTC) is an important factor. It can be calculated as the ratio of the concentration of pesticide residue in the consumers’ tissue to the pesticide concentration in the food. When TTC > 1. biomagnificatiou is expected to occur. Pesticides like DDT (TTC > 8), DDE (TTC > 9.7), and toxapliene (> 4.7) have a severe issue of biomaguifications in various food chains (Kay 1984, Evans et al. 1991). Residues of 13 organochlorine pesticides were detected in 36 species belonging to three lakes of north-eastern Louisiana, USA, and pesticide residue concentrations were more hi tertiary consumers like green-backed heron (Butorides striatus), and snakes, spotted gar (Lepisosteus oculatus), and largemoutli bass {Micropterus salmoides) as compared to the secondary consumers like bluegill (Lepomis macrochiras), yellow-crowned night- heron (Nycticorax violaceus), blacktail shiner (Notopis venustus), etc. and lowest levels were detected in primary consumers like crayfish (Orconectes lancifer) and threadfin shad (Dorosoma petenense), etc. (Niethammer et al. 1984). Biomagnification of dichlorodiphenyltrichloroetliane (DDT) along with its metabolite (4,4’-DDE) was detected in four fish species (Clarias gariepinus, Oreochromis niloticus, Tilapia zillii, and Carassius auratus) from Lake Ziway, Rift Valley, Ethiopia (Deribe et al. 2013). Recently, biomagnifications of DDTs, HCHs, and chlordanes in a food chain from Zhouslian Fishing Ground, China, have been reported with TTC value ranging from 4.17-9.77 (Zhou et al. 2018). Biomagnification of pesticides in non-target organisms and its detrimental effects on the physiological, morphological, and behavioural namre of amphibian, bird, etc. are well documented. Organochlorine pesticides inhibit gamma-aminobutyric acid (GABA) receptors in the brain and hamper the central nervous system of buds. Further, thinning of egg-shell by DDE, a metabolite of DDT, is another reason for the lower bu d population. Though organophosphate and carbamate pesticides do not have bioaccumulation issues, they are acute poisons. Pesticides have been reported to alter the hormonal balances, reproduction namre, birth defects, metabolism, immune suppression, and behaviour of birds (Oriss et al. 2000). Biomagnification of pesticides has resulted in adverse effects in humans also like the occurrence of cancer, tumor, neurotoxicity, child development, fertility, reproduction, etc. (Mostafalou and Abdollahi 2013). The overall impact of pesticides’ biomaguifications in terms of environmental and societal damages was nearly $12 billion per year alone in the USA. It includes wildlife loss (bird, fish, and others) of $2.2 billion, followed by water contamination worth $2 billion, loss due to development of pesticide resistance in pests costing around $1.5 billion, affecting public health valued $1.1 billion and crop losses worth $1.1 billion (Pimentel 2009). Hence, biomagnification of pesticides is a global problem and it needs to be addressed seriously for a safe and sustainable environment.
