Literature and Review
Arsenic contamination of groundwater in Bangladesh was first detected in 1993. (Safiuddin et.al). The problem then was thought to be limited to certain areas but later this notion was proved wrong. Subsequent investigations and reports disclosed more and more areas to be under arsenic contamination. High percentages of arsenic contamination in ground water have been detected in so many places that practically the menace now extends in varying degrees to nearly all of the country. (Financial express, 4 March 2000).
The greatest, most common source of exposure to organic arsenic is from food, particularly shellfish, meat, poultry, grain and dairy products. Food and drinking water together account for 99 per cent of total daily intake of arsenic through ingestion. The breakdown is roughly 84 per cent from food, 15 per cent from drinking water, less than one per cent from soil/dusts and a negligible amount from skin contact. (Ministry of the environment programs and initiatives, March 2001)
A least developed country like Bangladesh, saddled as it is with numerous problems, has been burdened with another and quite a formidable one because it involves drinking water that is basic to life and living. Arsenic presence in underground water - used heavily in Bangladesh for drinking and all household activities. (Financial express, 4 March 2000).
Not surprisingly, arsenic has become a top priority of the government and of aid organizations. Until recently, research and remediation focused almost exclusively on drinking water. Key links between arsenic and agriculture, specifically irrigated land and crops, had been largely overlooked. On average, a Bangladeshi adult drinks about 4 to 5 liters of water a day and consumes about 450 grams of rice. Assuming 200 ppb arsenic in the drinking water and about 0.5 milligrams per kilogram in rice grain, the total daily intake of arsenic would be around 1.2 milligrams, which may not be safe. (Arsenic and agriculture).
Islam et al. (2005) studied As levels in water, soil and crops at 456 locations in five sub districts during the Boro season of 2002. Soil, rice grain and straw samples were digested with concentrated HNO3 and H2O2.Total As in the digest and water samples were determined by flow injection hydride generation atomic absorption spectroscopy (HG-AAS). The average As concentration in the soil was 12.3 μg/g (range, 0.3-49μg/g), and the sub districts were classified according to soil concentrations: Faridpur> Tala> Brahmanbaria> Paba>Senbagh.the soils of Ganges river floodplain (Paba, Tala and Faridpur) had higher soil As levels compared to those of Meghna river floodplain (B.Baria and Senbagh). Mean total As levels of 4.6, 6.5, 7.2, 19.4 and 19.6 μg/g were found in Senbagh, B.Baria, Paba, Tala and Faridpur respectively. The mean As concentrations in Boro rice grain and straw in their study was 0.34 3.44 μg/g respectively.
Mazid et al. (2005) conducted a nationwide survey for As in soils, water and crops in seven hydrological sub-regions (HSR) namely- northwest (NW), north centre (NC), north east (NE), south west (SW), south centre (SC), south east (SE) and eastern hill (EH) areas of the country. A total of 135 unions under 67 thanas were selected for the sampling. As was determined using atomic absorption spectrophotometer equipped with hydride generation system (HG-AAS).
The concentration of As in shallow tube well (STW) water ranged from <1>650 μg/l. The highest mean As concentration of STW was observed in the SE/NE region while the lowest was recorded in the NW region.
The distribution pattern of As concentration in hand tube well (HTW) water was similar to that of STW, i.e., the highest in SE/NE regions and the lowest in NW region. The range of As concentration in HTW water varied from <1>530 μg/l. The level of As contamination in STW and HTW in the SW/SC and SE/Ne regions of the country was much higher than those of the NC and NW regions.
Among the three water sources the As concentration followed the trend: STW> HTW> surface water. The concentration of As in the surface water bodies (pond, river, canal etc.) ranged from 2 μg/l to as high as 63 μg/l. The interesting findings was that, the surface water bodies which were assumed to contain As-free water , exhibited high As values (>50 μg/l) particularly in the NW region.
The range of As concentration in surface soil varied from 0.2 mg/kg in the NC region to 67.5 mg/kg in the SW/SC regions. The highest mean soil As was recorded in SW/SC region which is located in the Gangetic and Meghna floodplain and the lowest was observed in the NC region located mainly in the Pliestocene terraces. The As concentration in the surface soil (0-15cm) was higher than that of the subsurface soil (15-30cm) in SW/SC, NW and SE/NE regions.
The concentration of As in rice grain ranged from 0.04 to 1.1 mg/kg. Except very few samples in the NW region, the rice grain As concentrations was much less than 1 mg/kg. The mean As concentration of rice grain was found highest in the NW region. On the average, the As content in rice straw was 7 times higher than that in grain.
Paul et al. (2005) in their global survey for As speciation in different rice varieties, found highly significant differences in total As concentration between Bangladeshi, USA, Indian and European rice. For total concentration of As, milled sub-samples (0.1-0.2g) were digested with nitric acid. No differences were observed between white and brown rice. USA long grain rice had the highest mean As level in the grain at 0.26 μg/g, and the highest grain arsenic value of the survey at 0.40 μg/g. This fitted well with other USA rice surveys, which range from mean values of 0.24 0.30 μg/g.
Bangladeshi wet season rice’s mean As level was 0.13 μg/g, ranging from 0.03 to 0.30 μg/g. This was similar to a previous Aman rice survey (Duxbury et al, 2003) with a mean arsenic grain level of 0.12 μg/g.
According to Farid et al. (2005) a study on the arsenic status of water, soil, rice grain and straw of a shallow tube well command area was done from the study area Brahmanbaria during the boro season of 2003. Soil, rice grain and straw samples were collected and analyzed, following tri-acid digestion, by HG-AAS and FAAS.
Four variety of rice (BR 28, BR 29, BR 36 and BINA 6) with four replications were grown with life duration of 137,154,140 and 159 respectively. They found As concentration in the grain- 0.550, 0.576, 0.507 and 0.612 μg/g for BR 28, BR 29, Br 36 and BINA 6 respectively. The As concentration in straw samples were 3.79, 3.81, 3.57 and 4.06 respectively. The findings of their study was that As content was higher in long duration varieties and lower in short duration varieties. The study also showed the range of As content in soil (3.21-24.4 μg/g), rice grain (0.16-1.20 μg/g) and rice straw (0.33-4.02 μg/g). The mean As content were found to be 9.42 μg/g, 0.43 μg/g and 2.00 μg/g for soil, rice grain and rice straw respectively.
Uddin et al. (2006) selected Feni district for sampling and to determine the impact of arsenic contaminated water on human health as well as overview of the extent and severity of groundwater arsenic contamination in Bangladesh.
They collected hair sample from the tube well water users belonged to two categories- below 12 years and upper 12 years of ages. From the experiment, it was reported that arsenic concentration in lower age categories was in the range of 0.33-3.29 μg/g and in the upper age categories the concentration was in the range of 0.47-6.64 μg/g.
Mohammad et al. (2007) conducted a study to estimate the total As present in vegetables grown in arsenic contaminated areas in Bangladesh. Various types of leafy and non-leafy vegetables were sampled from three As affected thanas of Bangladesh. Inductively coupled plasma mass spectrometry (ICPMS) was used for the determination of As.
The mean total As concentration in all vegetables were 173 mug/kg (range: 6-1316 mug/kg), 442 mug/kg (range: 1-8664 mug/kg) and 186 mug/kg (range: 3-1538 mug/kg) for Laksam, Muradnagar and Nabinagar, respectively. For Laksam, the highest mean As values observed were 463 mug/kg for sweet gourd leaf, 429 mug/kg for red amaranth and 369 mug/kg for green amaranth. The highest mean As levels were detected for arum root (1167 mug/kg) followed by water spinach (1001 mug/kg) and radish leaf (962 mug/kg) in Muradnagar. The maximum mean As concentrations found were 850 mug/kg for marsh herb, 437 mug/kg for arum root and 407 mug/kg for sweet potato leaf in Nabinagar. Their preliminary study on As speciation in vegetables showed that only inorganic As is present in vegetables which posed a real health risk to the villagers of that study area.
It should be worth mentioning that all the existing literatures so far completed on different areas of Bangladesh. But our project’s report undertakes an empirical investigation of arsenic impact on biodiversity. As Faridpur is one of most arsenic affected area of our country, so this area was selected for conducting this experiment of particular interest. All the samples were analyzed using Atomic Absorption Spectrophotometer equipped with Hydride Generation system.
