Determination of Arsenic Levels in Water and Soils from Ahero Rice Irrigation Scheme and in Ahero, Mwea and Imported Rice
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Date
2020-11
Authors
Aduda, Lucy
Journal Title
Journal ISSN
Volume Title
Publisher
Kenyatta University
Abstract
Arsenic contamination in irrigation water and soils is a major environmental health
hazard in the world. There is a major potential risk to human health through consumption
of agricultural produce grown in fields irrigated with arsenic contaminated water and
soils. Arsenic Levels have been analyzed in different crops such as rice, wheat, maize and
vegetables in different countries. Rice (Oryza sativa L.) is a crop cultivated mainly in
irrigated water hence its bioavailability to arsenic is much more than in other crops. This
study investigated the levels of arsenic in water and soils in Ahero rice irrigation scheme
and in locally produced and imported rice. Hydride Generation Atomic Absorption
Spectrometer was used in the analysis. Locally produced rice (Sindano and Pishori) was
sampled from Ahero and Mwea irrigation schemes while imported rice from India,
Thailand, and Pakistan was obtained from various market outlets Githurai, Eastleigh,
Ngara and Kenyatta. The level of arsenic in irrigation water and paddy soils was found to
be 0.0230 ±0.010 mg/L and 0.1504 ± (0.08) mg/kg respectively. There was a strong
positive correlation in arsenic levels in rice and soils from Ahero irrigation scheme
(r2=0.97, P<0.0001). A weak correlation was found between irrigation water and rice
(r2=0.16). The mean arsenic concentration in rice from Ahero and Mwea irrigation
scheme was 0.059±0.040 and 0.0371 ±0.03 mg/kg respectively. There was no significant
difference in the arsenic levels in Sindano rice from Ahero and Basmati (Pishori) rice
from Mwea Irrigation scheme. Basmati rice from Thailand had mean arsenic content of
0.126±0.001 mg/kg. The arsenic concentration was significantly higher than in Basmati
rice from Pakistan and India, with a mean of 0.075 ±0.001 and 0.062 ±0.01 mg/kg
respectively. The levels in the imported Basmati rice were significantly higher than
locally produced Pishori rice, a Basmati variety. Indian Sindano rice recorded
significantly lower levels (0.088±0.02 mg/kg) than those from Thailand (0.153 ±0.02)
and Pakistan (0.175 ±0.02 mg/kg). Arsenic levels was significantly higher in imported
Sindano rice from Pakistan and Thailand compared to locally grown Sindano rice
(p<0.0001). However, there was no significant difference in the levels in Indian Sindano
rice and the locally produced sindano rice (p>0.05). The levels of arsenic in rice from this
study were within the WHO recommended levels in rice grain of 1.0 mg/kg dry weight.
Though the levels are safe as per this study, chronic exposure from rice consumption
could be a human health risk. The information from the study will form a basis of setting
limits of arsenic levels in rice sold in the Kenyan markets.
Description
A Thesis Submitted in Partial Fulfillment of the Requirements for the Award of the Degree of Master of Science (Chemistry) in the School of Pure and Applied
Sciences of Kenyatta University, November, 2020
Keywords
Determination, Arsenic Levels, Water and Soils, Ahero Rice Irrigation Scheme