Review of Cadmium Pollution in Bangladesh

Background. Exposure to cadmium (Cd) is a global public health concern. The primary Cd exposure pathways are inhalation and ingestion. Globally, Cd production and consumption has increased, along with nickel-cadmium battery production, alloys, anticorrosive coatings, pigments, polyvinyl chloride stabilizers, semiconductors for solar cells, etc. After the end use of these elements, improper management may cause Cd pollution in different spheres of the environment and living organisms that eventually lead to adverse effects on human health. Objectives. The aim of the present study is to demonstrate the sources and routes of Cd that enter different environmental spheres, their concentrations, and describe associated human health impacts in Bangladesh. Methods. The present study searched a total of 304 peer-reviewed articles in the National Center for Biotechnology Information database, Science Direct, Web of Science, Springer Link, BanglaJOL, and university libraries and ultimately selected 71 articles. Afterwards, the relevant findings on Cd exposure through inhalation and diet and age-based impacts (i.e., adults, women, children and infants) in Bangladesh were combined. Finally, the results were processed with a cross-tabulation technique. Results. The present study found that Cd concentration in the local diet and river water is within the World Health Organization and Bangladesh Standard Testing Institute guidelines. Discussion. The concentration of Cd in sediments is comparatively higher than in river water in Bangladesh. Cadmium has been found in samples of foods, including leafy and non-leafy vegetables collected from different places in Bangladesh and may ultimately enter the human body via dietary intake of these foods. Consequently, individuals may be exposed to Cd and may be suffering from long-term adverse health effects. Conclusions. The comparison of concentrations in this study with national and international standards will assist with the formulation of effective pollution mitigation measures in Bangladesh. Competing Interests. The authors declare no competing financial interests.


Introduction
Anthropogenic activities, specifically rapid urbanization and industrialization, have contributed to the pollution of the environment with substantial amounts of solid, liquid and gaseous chemical elements, including hazardous elements such as arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu) and lead (Pb). 1 Other heavy metals with biological toxicity include mercury (Hg), zinc (Zn), copper (Cu), nickel (Ni), tin (Sn) and vanadium (V). 2 Trace metals are discharged into the soil through various pathways, including vehicle emissions, chemical production, coal combustion, municipal solid waste, and sedimentation of dust and suspended atmospheric pollutants. Other sources of atmospheric deposition include sewage irrigation, improper stacking of industrial solid waste, mining activities, and the use of pesticides and fertilizers, etc. 3 Moreover, heavy metals, except Hg, travel into the atmosphere in the form of aerosol and deposit into soil through natural sedimentation and precipitation. Heavy metals generated by industry, mainly in the form of gas and dust, are deposited in surrounding areas. 4 Cadmium is a heavy metal with high toxicity at very low exposure levels, and has acute and chronic effects on health and the environment. 5 It is non-biodegradable and once released into the environment, stays in circulation. 6 Cadmium in the form of sulfate and chloride salts of cadmium is comparatively more water soluble, more mobile in soil and can bioaccumulate. 7 Cadmium has different exposure routes, including diet, smoking, soldering, and drinking. Such intake modes can cause a variety of health problems, including kidney damage; impact bone metabolism producing endocrine effects by increasing the parathyroid hormone; Review fractional excretion of calcium and urinary N-terminal telopeptide; lung cancer; disturb hormonal interactions, thyroid hormones, and growth hormones; causes sex differences in nutritional status, and hormone stimulation; decrease zinc supply for fetuses; causes oxidative stress; as well as interferes with neuronal differentiation. 2,8,9,10-13 In addition, jewelry shop workers involved in soldering Cd are susceptible to pulmonary edema and are at risk of high blood pressure. 10 Furthermore, Cd exposure can negatively impact pregnancy, lactation and lead to undernourishment when breastfeeding. Cadmium inhibits the transport of calcium to breast milk. 5 Lastly, brain development in children can be hampered due to the Cd exposure. 5,6 Global Cd production totaled 23 200 tons in 2015 (Figure 1), a slight increase from the amount produced in 2014. Most secondary metal is recovered at Ni-Cd battery recycling facilities in Asia, Europe, and the United States. 14 According to the United States Geological Survey, 15,16 most (62%) of the world's refined Cd is produced in Asia and the Pacific (Australia, China, India, Japan, and the Republic of Korea), followed by Europe and Central Eurasia (Bulgaria, Germany, Kazakhstan, the Netherlands, Norway, Poland, Russia, and Uzbekistan) (23%), North America (Canada and Mexico) (11%), and South America (Argentina, Brazil, and Peru) (4%). The majority of global Cd consumption is generated from Ni-Cd battery production, followed by other end usages such as alloys, anticorrosive coatings, pigments, polyvinyl chloride stabilizers, and semiconductors for solar cells. 15 Natural and anthropogenic activities are the main causes of Cd contamination in different spheres of the environment. Table 1 summarizes the various routes and activities that cause Cd contamination in the environment and the associated effects on human health are presented in Table 2.
Due to various types of human activities such as tannery industries, pharmaceutical industries, low grade fertilizer application, automobiles, etc., the soils of Bangladesh are contaminated with high concentrations of Cd. As a result, the people of Bangladesh are exposed to Cd and experience various types Cd-induced health problems. Thus, the aim of the present study is to demonstrate the sources and routes of Cd that enter different environmental spheres, their concentrations, and describe associated human health impacts in Bangladesh. In order to formulate pollution mitigation measures in Bangladesh, comparisons should be drawn with national and international standards.

Methods
This study is based on research findings on Cd exposure from pertinent sources such as peerreviewed articles, textbooks, university theses, reports, etc. Studies were collected by prioritizing four aspects of Cd pollution and pathways (atmosphere, sediment, water and soil) along with corresponding health impacts on living organisms. Search Review terms included "Cd pathway", "Cd exposure", "heavy metals in river water", "trace elements in water", "Cd in river water" "Cd in river sediment", "Cd from industrial processes", "heavy metal contamination in soil" "Cd in food", "Pathways of Cd", "heavy metals in food chain", "Cd effects", "Cd effects on plants", and "Cd effects on human health". All of the studies were screened via abstracts to determine whether the study was relevant. Considered studies included a good description of Cd sources, routes and impacts on humans and other living organisms. After sorting out the related abstracts, full text articles or reports were assessed to identify studies which were fully or partially related to the study's objectives. The characteristics of reviewed papers, particularly the number of studies and their methods, are described in Table 3. Subsequently, studies that did not match the present study's aim were excluded, and finally 71 studies were selected for review. Selected studies were categorized based on their objectives. An overview of the literature selection process is shown in Figure 3. Lastly, findings were processed and analyzed with the Hosssain, Latifa, Nayeem

Results
Studies indicate that the major sources of Cd exposure in Bangladesh are tobacco smoking, food, particularly cereals, vegetables and seafood. 37 Diet is most likely the main source of Cd exposure in Bangladesh for those who live in rural environments with essentially no industrial contamination. The rice-based diet in the population contributes to 20-35 μg Cd daily. 5,32,33 These studies highlight the fact that elevated Cd concentrations in rice is a widespread problem and the present study has identified, for the first time, which Bangladeshi populations are exposed to excessively high levels of Cd in their diet. Previous studies have reported heavy metal contamination in surface water and aquifers along with human exposure in Bangladesh. Additional studies analyzing the pathways of heavy metals and contamination in the food chain found a considerable amount of Cd in the food chain (Table 4).
The present study scrutinized Cd concentrations in rivers across Bangladesh. The highest concentration of Cd was in the Turag River (17 mg/kg), followed by the Buriganga River (3.3 mg/kg), the Karnaphuli River (2.01 mg/kg), the Korotoa River (1.5 mg/kg) and the Bangshi River (0.61 mg/kg). Cadmium concentrations were comparatively higher in river sediments than in dietary products (Table 5). In addition, Cd concentrations in the water of these rivers were low in comparison to those of sediment, indicating that Cd accumulates in river sediment by deposition processes.

Discussion
In    Consequently, aquatic organisms have a high risk of exposure to Cd pollution that may ultimately enter the human body. Figure 4 illustrates the pathways of Cd exposure into the environment as well as their interlinkage among different media along with the human health impacts due to Cd exposure.

Conclusions
Cadmium concentrations in river water, sediments and diet are within the Bangladesh Standard Testing Institute and WHO limits. However, Cd can accumulate in aquatic species that are consumed by humans.
Hosssain, Latifa, Nayeem  Therefore, concentrations of Cd in water and sediment have been increasing due to bioconcentration and biomagnification, resulting in significant adverse health effects for invertebrates, fish and humans. It is important to investigate the root causes of Cd pollution and further experimental research is needed to more fully understand the level of Cd pollution in the environment, human tissue and the food chain. Moreover, legal actions and strong national policies are needed to reduce adverse health impacts of Cd pollution in Bangladesh.

Table 4 -Cadmium Concentrations in Foods in Bangladesh Across Studies
Hosssain, Latifa, Nayeem