A Critical Review of Heavy Metal Pollution and Its Effects in Bangladesh

Heavy metal, one of the most hazardous pollutant that can pose serious threat to human and environment. The concentrations of metals are increasing at an alarming rate due to boost of unplanned industrialization and urbanization. Though some metals are playing crucial role as micronutrients but the excessive amount exert negative impact at great extent. The existence of toxic heavy metals in the air, water and sediment can cause severe problems to all organisms because of their long persistence nature and bioaccumulation in the food chain. The present study reviews the various area of Bangladesh to make information on the sources of metal pollution, dissemination of metals in the environment and their possible effects on atmosphere, water, sediment, fishes and vegetables (plants).


Introduction
During last decade, rapid urbanization and industrialization have triggered some serious problems in environment. Heavy metals pollution is now a growing concern worldwide especially in developing countries [1] where rivers serve as dominant pathway for metals transport [2]. According to UNFPA [3], groundwater supplies most drinking water throughout the world, but many people use unsafe surface and groundwater sources. Though some people get access to water but not safe [4] because drinking water could be polluted with microorganisms [5], arsenic [6], polycyclic aromatic hydrocarbons (PAHs) [7], organic pollutants [8], nitrate and nitrite [9] and heavy metals [10]. Heavy metals are persistent, ubiquitous and nonbiodegradable in nature [11]. This characteristics of metals can pose chronic toxicity [12]. Considerable amount of metals accumulate in sediment and ultimately enter into the food chain through water, plants or leaching into groundwater. Heavy metals are responsible for brain damage or the reduction of mental processes [13] and central nervous function [14]. Moreover, it lower the energy levels [15], damage DNA [16] and alter the gene expression [17]. Skin [18], muscle [19], blood composition [20], lungs [21], kidneys [22], liver [18], heart [23], and other vital organs for human and other living organisms are being damaged by acute metals infestation. Every sector are now under the heavy metal pollution and its effects also inescapable. Industrialization increases the specific family income and reform the social structure but the negative effects compelled environment to be extinct.
[25] located in Dhaka, the heavily polluted river in Bangladesh. Fish, water and sediment are being contaminated by industrial wastes, municipal wastes and pesticides [26], [27]. The most common pollution is metal pollution. The heavy metal concentrations (Pb, Cr, Mn, Co, Ni, Cu, Zn, As, and Cd) in water and sediment were very high and in most cases, exceeded permissible limits recommended by the Bangladesh government and other international organizations [26]. According to Ahmed et al. [27] and Das et al. [28] the concentrations of some heavy metals in water, sediment and fishes exceeded the recommended value. Sikder et al. [29] mentioned that the concentrations of Al and Mn surpassed the limit set by WHO [30] and the concentrations of Fe, Cu, Zn, Cd and Pb found to be below the approved limit. Saha and Hossain [31] reported that the concentrations of Pb, Cu, and Zn were above the EPA guideline for heavily polluted sediment and the amount of Cd and Cr are fall in the criteria of moderately to highly polluted range. Mohiuddin et al. [25] found the concentrations of Cr, Pb, Cd, Zn, Cu, Ni, Co and As in water were significantly exceeded the admissible limit both in summer and winter season. The Buriganga River is considered partially a heavy metal polluted river and the water, sediment and fish are not fully benign for human health and ecosystem [32]. Ahmad and Goni [33] found the mean concentration of Cu, Fe, and Cd in irrigation water and Cd content in soil were much higher than the permissible limit but the metals level were below the allowable limit in vegetables set by the Joint FAO/WHO Expert Committee on Food Additives.    The Meghna River is also polluted with heavy metals because of rapid urbanization and industrialization. The water, sediment and fishes of the Meghna River contaminated with heavy metals. Heavy metals pollution is now growing concern in developing countries [ 18, Co: BDL-0.7 mg/kg respectively in fish and most of the metals were below the permissible limit set by some international guideline. Pb and Zn concentrations were found above the permissible limit in 15 fishes. Hassan et al. [44] reported that the concentrations of Cd, Cr, Mn and Zn in the Meghna river water are lower but Fe is higher than standard guidelines. According to USEPA [45] sediment quality guideline, sediment were heavily polluted with Ni.
The Shitalakshyaa River, the second most polluted river in Bangladesh located on the northwestern side of the capital links with the Buriganga River. Majority of the industries and factories are situated on the bank of this river. Due to the geographical location, various metals were found in excess amount. The amount of Al, Cd and Mn exceeded the recommended value set by WHO [30]. The concentrations of Pb, Fe, Cu and Zn were found below the permissible limit [29]. Rahman et al. [46] reported that the concentrations of heavy metals (Cd, Cr, Ni, Pb and Zn) are extremely higher than Bangladesh standard for drinking water [47].
The Khiru River located in Mymensingh, mostly polluted by industrial effluents. The concentrations of Cd, K and Na in water were much higher than the permissible limit though the concentrations of Cu, Zn and Pb were recorded below the permissible limit. In case of sediment, the concentrations of metals found within the limit except Cd. In fish muscle, the highest mean accumulation of Cu (3.65±1.04), Zn The Rupsha River, another important river of Bangladesh, also polluted by industrial discharge. The water of river endowed with heavy metals. The concentrations of heavy metals in the Rupsha River (passed through Khulna Metropolitan City) water were found within the permissible limits except for Fe [49]. Khulna city is the 3 rd largest industrial city after Dhaka and Chittagong in Bangladesh. Begum et al. [50] mentioned that the average Fe concentration was recorded 0.30±0.03 mgL -1 in the Rupsha River. Moreover, consumption of fish species from the Rupsha River is expected to exert health hazards for human being as the fishes are also contaminated by heavy metals. The Karnatoli River located near the Dhaka city that heavily polluted by tannery and textiles effluents. The concentration of heavy metals in river water varied due to seasonal changes. The recorded value varied for Zn: 0.62-68.47, As: 0.56-1.91, Cd: 0.13-1.53, Pb: 0.53-6.8, Ni: 4.2-8.2, Cr: 2.75-7.0, Cu: 8.6-48.14µg/L respectively. Some concentrations exceeded the admissible value [28].
The River Karatoa, the important river of Bangladesh also being contaminated by heavy metals. Zakir et al. [51] stated that the most dominant metals in midstream of the Karatoa River was Fe (0.89 µg mL -1 ) and Mn (0.012 µg mL -1 ) among 7 metals (Fe, Mn, Cu, Zn, Pb, Cr and Ni). Moreover, Mn exceeded the surface water quality standard (0.10 mg L 1 ) that indicates water pollution. [51]. The Bongshi River located adjacent to capital city and surrounded by many industries. The water of this river continuously being polluted from untreated waste water discharge. According to Sikder et al. [29], the concentrations of Mn and Cd exceeded the admissible limit and the value Al, Fe, Cu and Pb below the permissible limit.

Legend
The Balu River close to Dhaka city is also being polluted by industrial inputs and sewage. Discharge of wastewater from various industries without any treatment deteriorate river water quality badly [52][53][54][55]. The pollution with heavy metals worsen the situation. Rahman et al. [46] recorded the concentrations of Cd (0.011), Cr (0.020), Ni (0.02), Pb (0.009) and Zn (0.86) and found that the concentrations of all metals higher than Bangladesh standard for drinking water [47].
The Dhaleshwari River at Rajfulbaria in Savar, Dhaka is being polluted and contaminated by toxic metals. The major contributory factor that contributing heavy metals are industries adjacent to the river. The water and fishes of this river are contaminated with heavy metals that make these resources unsuitable for human consumption as the value of metals exceeded the standard limit. The concentrations of metals in S. aor were Cr: 1.458 mg/kg, Cu: 31.500 mg/kg, Pb: 18.776 mg/kg and Cd: 0.487 mg/kg of dry weight; in sediments were Cr: 27.393 mg/kg, Cu: 37.450 mg/kg, Pb: 15.797 mg/kg and Cd: 2.083 mg/kg, and in water were Cr: 0.130 ppm, Cu: 0.000 ppm, Pb: 0.201 ppm and Cd: 0.001 ppm. The level of concentrations in fish, water and sediment exceeded the FAO approved standard levels [27].

Heavy Metal Pollution of City Area
Dhaka the capital of Bangladesh. In present world, heavy metal accumulation in the soils is a concern of matter because of its potential health risks and detrimental effects on soil ecosystems [56][57]. Some heavy metals required for human and plants at certain level but excessive concentrations can be toxic [57][58] due to its nonbiodegradable nature [59]. Saha and Hossain [31] reported that the amount of Cr, Pb and Pb were found higher than recommended sediment quality guideline stated by USEPA but concentrations in the sludge were found below the limit provided by USEPA for land application of sludge. The road transports mainly contribute in polluting nearer soils by pollutant transfer through the atmospheric fallouts [60][61] or road runoff [60][61][62]. Most of the researchers mentioned that the impact of the traffic load on heavy metal contents in top soils and their inconsistency with distance [63][64][65][66][67][68]. The highest concentrations for lead was recorded in soil (0.1931 ppm) and in plants (0.1358 ppm) for highway on road at 0m distance. Contrariwise, the highest concentrations of lead was found in soil (0.0967 ppm) and in plants (0.0652 ppm) for railway on road at 0m distance. In both cases, the amount exceeded the recommended value set by WHO [63]. The maximum concentrations of heavy metals were recorded in both soil and grasses in the traffic congested area [69]. According to Naser et al. [70], there were prevalent differences in the concentrations of lead, cadmium and nickel for different plant species and soils at various distances and found in the order of nickel>lead>cadmium. Anthropogenic inputs and upward trends of industrial growth considered as the regulatory factors of environmental pollution. Heavy metal enriched in road dust directly related to industrial growth and upward trends of vehicle density in the street. According to Rakib et al. [71], most of the heavy metals (Pb, Cr, Zn and Cu) were observed to be higher compared to the recommended values. The metal concentrations ranged   [73][74][75][76]. As a result, this effluents may contain considerable amounts of potentially harmful elements and heavy metals like Fe, Cu, Zn, Mn, Cd, Cr, Pb etc. [77]. Islam et al. [78] reported that the concentration of Mn (0.68 to 0.72 ppm) exceeded the drinking water standards, even though Pb and Cu were recorded within the standard limit (0.0045 to 0.0085 and 1.33 to 1.58 ppm). Source: [78] Konabari industrial area located on the bank of the Turag River, Gazipur. There are many industries that discharge untreated wastes through the canal. The concentrations of toxic metals in wastewater and sediments of the industrial canals are much higher than that of the river water and sediments. In some case, the concentrations exceeded the permissible limit in sediment [81].
Savar, located just near the capital city that comprises of many isolated water bodies connected or not connected to the river system. The Bansi-Daleshwari and Turag, together form the drainage network of the Savar. The major part of this area are used for industrial activity. For this, the water and sediment adjacent to this area are highly polluted. Faisal et al. [82] showed that the average concentrations of Mn, Zn, Cr, Co and Cu were 584.68, 213.04, 190.33, 164.63 and 100.18 mg/kg respectively in topsoil. This values were noted above the permissible limit and this is the indication of environmental pollution. Aktaruzzaman et al. [83] recorded higher concentrations of Cd (1.00±0.68) mg/kg and Cr (2.32±0.84) mg/kg in the leafy vegetables.
Bhaluka industrial area in Mymensingh was infested with various textiles and garment industries. Textile industries soils contain high levels of lead than in textile effluents in Bangladesh [84]. The value of Cu (0.0405 ppm) and Pb (0.0003 ppm) were found lower than recommended level for industrial wastewater. Highest concentrations recorded for Zn (0.2-1.0 ppm) and lowest amount documented for Cr, Cd and Ni indicated that the river water is suitable for irrigation and aquaculture [85].
Bogra city is highly prone to environmental pollution because of its over population, rapid industrialization and urbanization. The pollution in soil with heavy metals may cause substantial changes in the composition of soil microbial community, badly affecting soil characteristics [86][87]. The average Cd and Cu concentrations in soil were higher than the recommended value [88]. Shambhuganj Gouripur is an upazilla under Mymensingh district endowed with many fresh water aquaculture ponds that contribute heavy metals. Heavy metals being intrinsic and natural elements can be toxic at low concentration [96], which mainly originating from fertilizers, animal manures, sewage sludge, agrochemicals and wastewater irrigation [97][98]. Sarker et al. [99] reported that the highest concentrations of Zn and Ni were found above the recommended value set by the US Environmental Protection Agency's [100] guideline in all sediment samples indicating severely polluted. Moreover, Cr falls under the moderately polluted range whereas Pb and Cd were recorded below the regulated level as per USEPA. In aquaculture farms, most of the fish feed contain maximum concentrations of Pb (8.57) and As (0.909) mg/kg though Hg and Cd concentrations were found to be low [101].
Chittagong the second largest city (port city) of Bangladesh. This city is highly polluted by industries, municipal wastes, two-stroke and diesel-run vehicles. Moreover, being a port city it is also polluted through spillage of ships and mechanized trawler. The concentrations of heavy metals in sediment recorded for Cd, Pb, Cu, Mn and Zn were in the range 0.5-1.9, 54-86, 25-50, 261-624 and 204-330 mg kg −1 respectively, indicate contamination of soil with heavy metals [102]. Besides sediment, air of the city also polluted by heavy metals. Ahmed et al. [103] reported that the concentrations of heavy metals in ambient air of different locations in Chittagong city exceeded the threshold limit. Parvin et al. [104] recorded higher concentration of Pb and Cr in vegetables (Green arum leaves, jute leaves, water spinach, bottle gourd, wax gourd and sweet gourd collected from industrial area (Nasirabad, Agrabad, Vatiary and Chalkbazar).

Heavy Metal Pollution of Coastal Area
Ship breaking area in Chittagong is highly affected by heavy metal. The sediment samples were moderately to heavily polluted with Pb, Cu, Zn and Cr but the concentrations in water were found below the permissible limit except Cr (0.511± 0.284) mg/l [83]. Bay of Bengal coast's sediment (Matamuhuri, Moheshkhali, Bakhkhali, Naf Rivers and St. Martin's Island) was highly polluted with heavy metals that originated mainly from domestic and industrial discharges, gas production plant [110], agriculture and shrimp farming. Heavy metals are being found in water though some preventive actions being applied [111][112][113]. The heavy metal concentrations in the marine surface water mostly exceed the criteria of international marine water quality [110]. Higher concentrations of Cd (.07) and Pb (0.75) µg/g were recorded from Bay of Bengal coast that exceeded the Environmental Quality Standards of Bangladesh (Cd: 0.05 and 0.10 µg/g) though Zn, Cu, Mn and Fe concentrations were recorded within admissible limit [114]. Source: [115] Sundarbans, the largest, richest (biologically) and most widespread mangrove forest in the biosphere. It is popularly known as world heritage site. Heritiera fomes (3.5 million), ecologically dominant and economically valuable tree species in Sundarbans arena. But unfortunately, millions of the trees and people in Sundarbans are being affected by heavy metal contamination [116]. According to Chaffey et al. [117], 45.2 million of Sundri trees have been affected in Sundarbans.

Effects on Aquatic Animals and Human
The metal pollution of aquatic ecosystems is increasing due to the rapid and unplanned urbanization and industrialization [118][119][120][121][122]. Heavy metals are very harmful for aquatic animals [123] and human health [124] due to their toxicity, long-term persistence, and subsequent accumulation [123]. As a result, water, sediment and fish are not fully safe for human health and ecosystem.
Fish are important part of the human diet that have been severely polluted with heavy metals in recent time. Heavy metals pollution destroy the fresh water aquatic ecosystem especially ruined diversified fish community which contributes an important share in the domestic protein demand of the country [125]. Fish and crayfish are used as bio indicators of metal pollution due to their assistance in understanding of the risk to the aquatic ecosystems and to humans [126][127][128]. Fishermen and adjacent local people are suffering from various diseases like irritation and skin disease [34]. Moreover, in human body heavy metals can disrupt function in heart, brain, kidneys, bone and liver. Heavy metals (Pb) reduced cognitive development and intellectual performance in children, increased blood pressure and cardio vascular disease in adults [130]. High concentrations of metals can cause cancer of the lung and nasal cavity [131]. Table 12. Negative effects associated with heavy-metal exposure and toxicity.

Metal
Acute toxicity Chronic toxicity Reference (s)

Arsenic
Bloody urine, GI discomfort, diarrhea, headaches, vomiting, convulsions, coma, and death Skin lesions, blisters, Blackfoot disease; organ failure/damage; diabetes; cancer and mutagenic properties [132][133][134][135] Cadmium Hepatic, pulmonary, and testicular injury Renal and bone injury (osteoporosis); carcinoma (primarily prostate and renal); toxicity to other organs [136][137][138] Chromium Vomiting and diarrhea; hemorrhage and blood loss in GI Tract Liver/kidney necrosis; skin ulcers, "chrome holes," irritative dermatitis; ulceration and perforation of the nasal septum; nasal, pharyngeal, and gastrointestinal carcinomas [139][140] Lead Neurobehavioral problems: impulsivity, distractibility, and short attention span; mild fatigue; headaches, nausea, vomiting Antisocial behaviors; impaired hemoglobin synthesis; impaired renal function; deafness, blindness, retardation; decreased IQ, memory loss; decreased libido, fatigue [141][142][143][144][145] Mercury Impaired neurodevelopment; loss of IQ; decrease in memory, attention, language, and visual-spatial perception tests; associations with autism and ALS Impaired neurodevelopment; loss of IQ; decrease in memory, attention, language, and visual-spatial perception tests; associations with autism and ALS [146][147][148][149][150] Source: [151] Plants the primary producer can absorb heavy metals from soil [152][153] and these metals contaminate the soil [154]. Excessive concentrations of heavy metals in sediment can affect growth of plants by disrupting metabolic functions, physiological and biochemical processes, inhibition of photosynthesis, respiration and degeneration of main cell organelles, even leading to premature death of plants [155]. Though some metal play role as micronutrients in plants [156] but they can be toxic at high concentrations [157] which compelled plants to produce reactive oxygen species that damage plants cell [158]. Ultimately, metals enter into human body in the form of vegetables and cause death [159]. Nabuloa et al. [62] recorded that leaves of roadside crops can amass trace metals at high concentrations, causing a serious health risk to consumers and poisonous to animals grazing on the plants [160]. Plants, prolonged exposure to heavy metals leads to cellular damage and disturbance of cellular ionic homeostasis. Top-dying of Heritiera fomes (Sundri) in Sundarbans directly linked with Exchangeable Sn, K, Pb, Sr and Zn [161].

Conclusion
From the findings of the present review, it is evident that water, aquatic organisms and roadside dust are being polluted increasingly. Being long persistent metals in nature these substances exacerbating the health problems both in human being and fish. As a consequence, different fatal and chronic diseases find their permanent residency in living organisms through the process of biomagnification. Above study proved that, industrial area are adversely affected by heavy metals rather than non-industrial area. For the meaningful and sustainable development of the country industrial growth needed badly but this development should be environment friendly. Industries should not discharge their effluents directly to the river water rather they must use Effluent Treatment Plant (ETP).