The impact of current agricultural practices on the produce: chemical analysis of rice and reservoir water in Sri Lanka
Paddy rice (Oryza sativa L .) is the principal food of Sri Lankans. Rice provides 30% of the dietary energy and 20% of the dietary protein intake of Asians (World Health Organization FSD, 2002). It is a well-known fact that rice is contaminated with toxic chemicals and trace elements due to the unrestrained use of agrochemicals in cultivation and the use of contaminated water to irrigate paddy fields. Heavy metals that have been found to be present in high levels include Cadmium (Cd), Arsenic (As), Lead (Pb), Nickel (Ni), Zinc (Zn), Copper (Cu) and Mercury (Hg).
Cadmium is a well-known carcinogenic heavy metal. It also contributes to anaemia, hypertension and renal, pulmonary and skeletal disorders (Khaniki and Zazoli, 2005). The current tolerable exposure level of Cd is 25 μg/kg body weight per month (Satarug, Vesey and Gobe, 2017). The main sources of Cd in rice are phosphate fertilizer and contaminated water.
The dietary intake of Cd in Sri Lanka is chronically high (Bandara, 2008). The study conducted by Bandara et al. (2008) in the Anuradhapura district shows that the Provisional Tolerable Weekly Intake [an estimated amount of the chemical with no intended function that can be ingested weekly over a lifetime without appreciable health risk ] of Cd is 8.702–15.927 µg/kg body weight for 5–50 years. Further in the study, it has shown that dissolved Cd in reservoir water ranged from 0.03 to 0.06 mg/l, which is a 19-fold increment over the maximum contaminant level set by the WHO (0.003 mg/l). Cd content in lotus rhizomes was 253.82 mg/kg which is a common curry in Sri Lankan meals (Bandara, 2008).
Another survey conducted by Meharg et al. (2013) using rice samples from 12 countries reported a mean Cd concentration of 8µg/kg in Sri Lankan rice which was second only to Bangladesh (mean=99µg/kg). A study published in 2020 shows that the average concentration of Cd in rice was 0.080 ± 0.130 mg/kg. Although almost 97% of the samples were below the Codex limit for polished rice (0.4 mg/kg), five samples had Cd concentrations of 0.488 to 0.727 mg/kg, exceeding the Codex maximum permissible level by 1.25 to 1.75 times, respectively (Liu et al., 2020).
Arsenic levels in the groundwater and surface water of the country are negligible (Chandrajith et al., 2011). But a study conducted by Jayasumana et al., (2013) shows an elevated level of As (20.6-540.4 μg/kg) in agrochemical-dependent cultivations compared to cultivations done without using agrochemicals (11.6-64.2 μg/kg). Another study published in 2020 shows an average concentration of As of 0.077 ± 0.040 mg/kg which was considerably lower than the maximum Codex standard level (0.200 mg/kg). But two samples from the Northern Province contained As at 1.1 times that of the Codex maximum permissible level (Liu et al., 2020).
The average concentration of Pb in Sri Lankan rice was 0.031 ± 0.052 mg/kg. The Pb concentration in three samples from Central, Northern and Western provinces exceeded the Codex threshold (0.400 mg/kg) by 1.5 to 2 times
In summary, the available literature and scientific data attest to the fact that the rice in the local Sri Lankan market contains heavy metals, probably due to the uncontrolled use of agrochemicals for paddy cultivation and irrigation using contaminated water. This is an alarming finding given the health consequences following long-term exposure to these chemicals, even at low concentrations. One of the main concerns in Sri Lanka currently is chronic kidney disease of unknown aetiology (CKDu), the incidence of which is rising among the agricultural communities especially in the North Central province. Although the cause of this disease is yet unidentified, heavy metals have been implicated in the pathogenesis as high levels of these have been found in affected individuals (Kulathunga et al., 2019). Therefore, timely action is required from authorities to regulate agricultural activities in order to minimize their harmful effects on human health. In the Sri Lankan context, this would not prove difficult as the country has a long history of ecological agricultural practices which are safe for both humans and the environment.