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.