ARSENIC IN FOOD CHAIN: REMEDIAL POSSIBILITIES S.M. Imamul Huq1, Ray Correll2, Ravi Naidu3, J.C. Joardar1, Marzia B.Abdulalh1 and Umme K.Shila 1 1Department of Soil, Water & Environment, University of Dhaka, Dhaka-1000, Bangladesh; 2CMIS, CSIRO, Adelaide, Australia, 3University of South Australia, Adelaide, Australia
Our hypothesis is that water-soil-crop-food transfer, cooking water and the direct ingestion of contaminated water are the three major exposure pathways to As
Rationale • High yielding variety (HYV) rice cultivation is encouraged-cereal production increased from 11 m t in 1975 to 25 m t in 2004. • HYV cultivation mostly needs irrigation water • 85% of total groundwater withdrawn is utilized in agricultural sector • Most groundwater is contaminated with Arsenic
Rationale-contd. • ~ 40% of the NCA is under irrigation – Boro Rice, Wheat, Vegetables need irrigation • ~20% crop loss has been reported due to high arsenic concentration in growth medium • Boro rice accounts for about 37% of total rice production in Bangladesh
FAMILY AGRI FIELD INDIVIDUAL WATER SOIL PLANTS/VEGETABLE GRAINS GPS Symptoms NUTRIOTIOANAL STATUS QUANTITY OF DRINKING WATER QUANTITY OF FOOD FOOD HABIT INCOME/MONTH ARSENIC GENERAL ARSENIC FOOD CHAIN TRANSFER PATHWAY NUTRITION SYMTOMS COOKING WATER QUALITY COOKED FOOD UNCOOKED FOOD VEGETABLE FROM KITCHEN GARDEN DRINKING THROUGH FOOD DRINKING WATER SOURCE SOIL FROM KITCHEN GARDEN ARSENIC REMEDIATION METHODOLOGY
Dietary intake was assessed by surveying the food consumption of villagers. A questionnaire was developed that included a list of all the dietary components Overall 60 households from 3 districts were interviewed in the initial survey A subsequent survey interviewed an additional 255 households from 30 villages Over 100 food types were recorded The two most important components were drinking water and cooking water, followed by rice and other vegetables
To assess the contribution of As-contaminated water to the cooked rice (Bhat), a laboratory experiment was carried out with 13 different rice samples procured from a local wholesale market. • All the rice samples showed levels of As below the detection level of the machine (2 g/kg). • 5.0 g each of the rice samples were cooked in the laboratory by two conventional methods; • Method I – 50 ml water and rice were cooked so that all the water is absorbed by the rice by the time it is well cooked (Bhat);
Method II – 100 ml water was used and when the rice is well cooked, the liquid starch is decanted. • The rice samples were cooked with fresh water or spiked water (equivalent to 50 g/L As). • The As contents of the cooked rice (Bhat) and the liquid starch were also estimated • The results were then extrapolated to the average consumption of cooked rice (Bhat) per person per day (450 g of uncooked rice).
The basic model for the daily arsenic load LW from water was sum of drinking and cooking water sources The basic model for the daily arsenic load LF of food was
The total daily arsenic load L was simply the sum of arsenic load from water and food where wi is the daily intake of the ith food type, mi the moisture content , ci the arsenic concentration and ai the bioavailability. The distribution of each wi was calculated as the product of a binomial distribution, indicating whether that food was eaten on that day, multiplied by a lognormal distribution fitted to the data obtained from the diet survey. The concentration was modelled using a lognormal distribution. The moisture content and bioavailability were modelled using a Beta distribution.
Scenario 1: typical diet + safe water • As safe drinking-water in conjunction with a typical diet is considered. Water near the maximum value within the Bangladesh guideline of 0.05 mg/L–1 was chosen, a standard error of 0.02 mg/L–1 was allowed. It was assumed that the cooking water is gathered from surface water because that is known to have a low As content and biological contaminants would be destroyed in the cooking process • Food consumption and the As content of food are assumed to be some average values, but with the As content of 0.25 mg/kg–1 • The simulations show the mean As load of the average villager is 161 μg/day–1, with 104 μg/day coming from the water. Of the remaining 57 μg/day–1, 49 μg/day–1 came from rice and 8 μg/day–1 from vegetables • In this scenario there was less than 1% chance of exceeding the 220 μg/day–1 guideline
Scenario 2: typical food + 3 L drinking-water This scenario differs from Scenario 1 in that the drinking-water consumption is assumed to be 3 L/ day – a very reasonable scenario in the hot weather of Bangladesh. The average load was then 212 μg/day–1 with a 6% chance of exceeding the 220 μg/day–1 limit.
Scenario 3: typical food + 3 L good drinking-water In this scenario, very good water (As content 0.005 mg/L–1) is considered The food (including rice) is assumed to be typical with the same distribution as in Scenario 2 Under these conditions As load does not present a risk.
Scenario 4: high As rice diet + 3 L drinking-water This scenario assumes 3 L/day of drinking water with 0.05 mg As/L–1 but rice, the dominant component of the diet, is assumed to have the highest average As content found in any district – 0.437 mg/kg–1 When that value is used in the simulations, the mean load is 304 μg/day–1 and effectively all cases exceed the 220 μg/day limit Rice contributed to 144 μg/day–1, approximately 65% of the 220 μg/day–1 limit
Scenario 5: high leafy vegetable diet + 3 L good drinking-water - This scenario is equivalent to Scenario 2 but with the typical meal of 152 g of arum eaten every second day. - This fairly minor perturbation in the diet increases the daily average load to 219 μg/day–1, with 25% of cases exceeding the 220 μg/day–1 threshold. - Similar results would be obtained by increasing the consumption of other leafy vegetables that have been found to accumulate elevated amount of As
Even if a rice sample does not contain any detectable amount of As, the cooked rice (Bhat) however, contains a substantial amount of the element when it is cooked with As contaminated water • The amount of As in cooked rice (Bhat) plus an average consumption of four litres of the same source of water as drinking water with the Bangladesh standard of 50 g/L As along with As rich vegetables is sufficient to bring the value of daily ingestion of As above the MADL of 0.22 mg per day
The per cent of population risking the exposure to excess of MADL, has been calculated • For Jessore (representing Gangetic Alluvium) 32% of the people are above the MADL • In a separate study, with a different model, it has been calculated that in Jessore, the daily ingestion of As in adult is more than 4mg and in children it is more than 2 mg • In Rangpur area the value is only 2% • Extrapolated for the whole country (as represented by the average of the two areas), the value comes to 19% of the population
The above information asserts that arsenic ingestion in human body besides drinking water is through food chain • Based on our survey and modeling studies, it is apparent that food can contribute to more than a third of the total daily intake of As • Crops receiving arsenic contaminated irrigation water take up this toxic element and accumulate it in different degrees depending on the species and variety • While much work still needs to be done to get a better picture of exposure to As of human in Bangladesh our preliminary results demand further detailed study and also the need for development of strategies that minimize the water-soil-plant transfer of As.
In a recent study, Williams et al.(2005) have found that the mean arsenic level from Bangladeshi rice was 0.13 mg As kg-1, in a range from 0.03 to 0.30 mg As kg-1. They have also found that the main species detected in Bangladesh rice were As III, DMA V, and As V of which more than 80% of the recovered arsenic was in the inorganic form.
Bioremediation by algae Bioaccumulation was significantly positive;y = 6.521+49.287x, R = 0.9578**
Consequence of bioremediation As accumulation in Kang kong ( Ipomea aquatica ) after 30 d
Phytoremediation of Soil Arsenic(byMarigold-Tagetes patula) Ref: Imamul Huq, S.M. et.al., 2005. Marigold (Tagetes patula) and ornamental arum (Syngonia sp.) as phytoremediators for arsenic in pot soil. Bangladesh J. Bot. 34(2):65-70.
Phytoremediation of Soil Arsenic(byOrnamental arum-Syngonia sp.) • Ref: Imamul Huq, S.M. et.al., 2005. Marigold (Tagetes patula) and ornamental arum (Syngonia sp.) as phytoremediators for arsenic in pot soil. Bangladesh J. Bot. 34(2):65-70.
CONCLUSION • We conclude that the largest contributor to As intake by Bangladesh villagers in affected regions is contaminated drinking-water • The second-largest contributor is food, notably rice • Followed by vegetables
CONCLUSION (contd.) • Dietary loads of As in Bangladesh needs to be considered a public health problem • Steps to reduce this load, on the farm and in the kitchen, are recommended as a matter of urgency • Possible mitigation strategies need to be assessed • Further detailed study and need for development of strategies that minimize the water-soil-plant transfer of As are proposed
Arsenic in the Environment Arsenic is an element that occurs naturally in the environment. Since arsenic is a natural part of the environment everyone is exposed to small amounts. These sources are shown below. Bangladeshi people are likely to be exposed to higher amounts of arsenic through drinking arsenic contaminated water or consuming foods like vegetables that accumulate high concentrations of arsenic.
Acknowledgement • The authors acknowledge the services rendered by the Bangladesh Australia Centre for Environmental Research (BACER-DU) and the MoE, the Govt. of Bangladesh and ACIAR, Australia for financing part of the research.