Heavy metals are non-biodegradable materials which cause serious carcinogenic effects on animals and human body [26]. Fish and fishery products may be contaminated by heavy metals as fishes live in the aquatic environment. Reference [21] studied the level of heavy metal contamination in the dried fish found in Cox’s Bazar local market. Comparatively higher amount of heavy metals was accumulated in Mola (Amblopharyngodon mola), Rupchanda (Stromateus chinensis) and Chhuri (Trichiurus lepturus) than other fish species (Loitta, Shundori, Fatra, Phasa). Iron (Fe) was found in greater concentrations compared to other heavy metals [21]. Also, reference [27] found more or less similar amount of cadmium, chromium and lead in the sun dried Loitta (Harpodon nehereus) and Churi (Trichiurus haumela), which is higher than the Maximum Allowable Limit of reference [26] [28] [29]. Besides, the excess amount of these three heavy metals (Cd, Cr and Pb) were also found in dried taki, tengra, shol and punti collected from the local market of Natore district of Bangladesh [30] (Table 1). Similarly, Cd, Cr and Pb concentration in Silver pomfret (Stromateus cinereus) and Perch (Lates calcarifer) purchased from the local fish markets of Cox’s Bazar exceeded the maximum allowable limit [31] (Table 1). Moreover, reference [32] investigated the heavy metal concentration in dried boal (Wallago attu) collected from Mymensingh local market. They observed that the Chromium (Cr) concentration was 0.068 ppm, which exceeds the acceptable limit for human consumption, according to reference [28].

These heavy metals are accumulated in fish and other aquatic organisms from aquatic environmental pollution due to enhanced urbanization, industrialization, population number and over exploitation of mother nature [33] [34] [35]. Most of the heavy metal elements are cumulative poisons, that is, those that cause injury to health through progressive and irreversible accumulation in the body as a result of ingestion of small amounts repeatedly [36]. Cadmium affects kidneys and causes symptoms of chronic toxicity, including impairment of kidney function, poor reproductive capacity, hypertension, tumors and hepatic dysfunction [37]. Excess exposure to Pb may cause nervous system damage,

paralysis, and pain in the legs [38]. Moreover, Cr is also injurious to health. If eaten regularly with contaminated fish and fishery products, Cr cause irreversible problem in stomach, renal disease and overall health risk [31]. Many countries in the world are taking various types of mandatory and voluntary actions to prevent aquatic pollution by hazardous chemicals to ensure food safety, especially for aquatic food products. The food regulatory and health authority of some developed countries have taken serious measures and adopted a maximum allowable limit for hazardous substances by considering their effect on human health [32].

Insect infestation is a major problem during fish drying [39]. Fish processors have usually taken various preventive measures to protect the dried fish from insect infestation [16]. Among them the most popular preventive measure is the use of hazardous chemical pesticides without considering the lethal effects of these pesticides on consumer body. DDT and Nogos are most commonly used in dried fish as pesticides to prevent insect infestation [5]. In another study, reference [15] found that DDT and Heptachlor are used in dried fish of Bangladesh as a mixture of organochlorine (Table 2). DDT is locally known as white powder. These chemical pesticides are effective to protect fish from insect infestation, but they are associated with human health hazard and also hazardous for the environment [12] [20].

In the last few years, application of a number of health hazard pesticides (e.g. dichloro-diphenyl-trichloroethane, heptachlor) has been exposed nakedly in the dried fish industries [16]. However, the maximum recommended limit (MRL) of DDT is 50 ppb and the MRL of heptachlor, endrin, aldrin and dieldrin (Dirty Dozen) in food is 10 ppb [40]. Exceeding this limit of these chemicals causes a long-term health effects and a variety of diseases to the consumers. Also, reference [15] screened DDT concentration ranges from 3.038 to 874.966 ppb and heptachlor residue ranges from 0.682 to 5.464 ppb in the dried Bombay duck (Harpodon nehereus), Ribbon fish (Trichiurus haumela) from 4 different places of Dhaka and Chattogram. It can be assumed from this study that a mixture of insecticides is still used in the dried fish of Bangladesh. In another study, the DDT and heptachlor concentration in dried Anhovy (Septipinna phasa) and Croaker (Johnius dussumieri) were 19.416 ppb and 18.306 ppb, and 16.404 ppb and 14.856 ppb, respectively [41], which exceeded the MRL (Table 2). Similarly, the excess amount of heptachlor was found in dried Chinese pomfret (Pampus chinensis) and Indian salmon (Polynemus indicas) [42] [43]. It was observed that heptachlor is a carcinogenic to human (B2) and it can pass to unborn baby from pregnant mother’s through the placenta [44].

In another study, the mean concentration of DDT in dried Bombay Duck (Harpodon nehereus) collected from Borobazar and Reajuddin Bazar stations, Chinese Pomfret (Pampus chinensis) from Kalishpur and Reajuddin Bazar, Shrimp (Penaeus spp.) from Borobazar and Moilapara were ranged from 261.89 ppb and 874.35 ppb; 250.47 ppb and 877.82 ppb; 161.67 ppb and 589.97 ppb, respectively [18]. For ribbon fish (Lepturacanthus savala), the DDT residues were 141.43 and 253.68 ppb that detected from Reajuddin Bazar, Borobazar and Moilapara station, respectively, which were higher than the acceptable limit recommended by WHO. DDT concentration in the Ribbon fish (Trichiurus haumela), Bombay duck (Harpodon nehereus) and croaker (Johnius dussumieri) were ranged from 130.85 to 153.47 ppb, 125.21 to 181.4 ppb and 119.86 to 208.65 ppb, respectively. The mean concentrations of DDT were found at a lower amount in Penaeus sp. than the other, which indicates that the concentrations of DDT in

ND: Not determined; MRL of DDT is 50 ppb, MRL of heptachlor is 10 ppb.

dried fish from Bangladesh were higher and may cause chronic disease and potential long-term risk to human health [45].

A significant amount of multiple pesticides (DDT, endrin, aldrin, dieldrin) have been found in various dried fishes such as tengra, taki, shol, chingri, prawn, kaski, chapila, gonia, mola and puti [20] [46] [47] [48] (Table 3 and Table 4). The presence of multiple pesticides in dried fish could be explained as a single pesticide used by dried fish producers and another might be used by the dried fish value chain vendors for long-term preservation [16] [20]. Besides, reference [49] reported that more than 60.19% fish and fisheries products contain pesticide residue. Moreover, contaminations of pesticide in fish and fisheries products varied geographically. DDT, Heptachlor, Diazinon, Chlorpyriphos, Acephate, Qunalphos, Carbaryl, etc. were abundant in Dhaka, Chattogram and Rajshahi divisions [49]. Also, reference [16] screened 92 dried fish samples obtained from eight districts of Bangladesh and found that 42 samples were contaminated with DDT, Dimethoate, Fenitrothion, Chlorpyrifos, Acephate and Diazinon residues, which are extremely hazardous for humans and the environment.

Dried fish contaminated with DDT is responsible for chronic health hazards as DDT is a slow poising substance and shows vertical transmission from generation to generation through breast milk [50]. It is the most concerning issue. Processors, exposed to DDT occupationally have an increased incidence of non-allergic

MRL of DDT is 50 ppb.

MRL of Endrin, aldrin and dieldrin is 10 ppb.

asthma [51] and have direct links with diabetes [52], cancer [53]. A number of studies have argued that the accumulation of DDT in human body before puberty increases the risk of breast cancer for the women [54]. At present, importing as well as producing the “Dirty Dozen” pesticides is prohibited in Bangladesh. Now a day, there is no legal use of any persistent organochlorine pesticides in Bangladesh, however, some old stocks may be available and some may be available through other unknown sources [20] [55].

Fish lipids containing polyunsaturated fatty acids are highly unstable and susceptible to reaction with atmospheric oxygen and produce hydroperoxide compounds and free radicals cause off flavor and off odor in dried fish. The higher amount of hydroperoxide compounds and free radicals indicate the poor quality of a food product [56] [57]. Table 5 shows rate of lipid oxidation in dried fishes available in Bangladesh. The peroxide values of the traditionally dried 8 marine fish samples ranged between 46.80 and 82.70 meq/Kg oil [58]. Almost all values are above the acceptable limit indicating whole marine dried fish can be considered to be spoiled for most uses. More or less similar findings have been reported in the cases of dried tengra [22] and kholisa [23] and sun dried puti, chapila, taki [59]. Moreover, the excess amount of acid value was also found in dried kholisa, punti, chapila and taki [23] [59]. In general, the rate of oxidation increases with the increasing temperature. Other factors may be relative humidity of environment and absorbing moisture from atmosphere. The increased peroxide

and acid value in the dried products are susceptible to rapid oxidation during processing, drying and storage under abused influencing conditions. The abused influencing conditions include inappropriate packaging causing off flavor and off odor [22] [23] [60] [61] [62] which reduce the product value to the consumers. Oxidized dried fish products are not safe for human consumption [63]. The lipid oxidation primary products in fish reduce its protein digestibility [64] and formation of secondary oxidation products can cause aging, membrane injury, cardiovascular diseases, atherosclerosis and tumor growth [65] [66].