Assessment of Arsenic in Rice Growing Areas of Pakistan

The natural occurrence of arsenic in ground water constitutes a setback in the provision of safe drinking water to millions of citizens in Asia. At least 60 million people live in arsenic -affected regions and many drink arsenic-contaminated water on the daily basis. Pakistan Council of Research in Water Resources (PCRWR), has conducted several research studies to identify and quantify arsenic contamination of ground water being used for domestic, agricultural, and industrial consumption specifically in Punjab and Sindh provinces. Arsenic ingestion is often estimated from water intake alone, although it is increasingly apparent that an additional loading arises from arsenic in food, especially from paddy rice grown with contaminated irrigation water. Soils thus irrigated may accumulate arsenic to phytotoxic levels, creating a problem of latent effects on crop yields.

Arsenic is a highly toxic element that is naturally present in higher levels in ground water drawn from alluvial soils (i.e. those deposited by rivers). The Indus valley is therefore one of the regions in the world where this hazard is ever present. In Pakistan arsenic contamination is prevalent mainly in Punjab and Sindh provinces, and the hazard in drinking water drawn from wells is well known. However, hew research has recently come to light indicating that arsenic can be toxic over the longer term at levels much lower than previously considered. As a result there are new concerns regarding the total dietary exposure to this element, and this has raised the issue of the safety of some food crops which may be grown in affected areas when irrigated with ground water.

Most investigations have focused on the arsenic risk from drinking water, but there is now widening interest in whether this poison can also be passed on in rice, through irrigated fields. Human exposure to arsenic (As) via rice consumption is of increasing concern. Rice is one of the most important food crops around the world and feeds over half of the global population.

Pakistan being an agro-based economy has natural abundance of all agricultural products including food items. Rice is the third largest crop after wheat and cotton. It is grown over 10% of the total cropped area and is highly valued cash crop as well as major export item. It accounts for 6.7% in value added in agriculture and 1.6% in GDP. Pakistan grows enough high quality rice to meet both domestic demand and allow for exports of around one million ton per annum. Pakistan exported about 3.4 million tonnes of rice in 2012, earning about US$1.8 billion. The establishment of international limits on arsenic in rice could potentially impact on this important export market for Pakistan.

On the basis of the occurrence data collected, the preliminary findings of this study have revealed that arsenic contamination risk from irrigation water to food chain has not reached alarming proportions yet, however; there is a need to deal with the possible threats posed by arsenic contaminated irrigation water. Distribution of arsenic in major rice varieties specifically of export quality is not a critical concern at present. However, the results of this study calk for careful implementation of the irrigation system modernization taking ground water quality in due consideration.