Assessment of potentially toxic and mineral elements in paddy soils and their uptake by rice (Oryza sativa L.) with associated health hazards in district Malakand, Pakistan

Rice, a primary food source in many countries of the world accumulate potentially harmful elements which pose a significant health hazard to consumers. The current study aimed to evaluate potentially toxic and mineral elements in both paddy soils and rice grains associated with allied health risks in Malakand, Pakistan. Rice plants with intact root soil were randomly collected from paddy fields and analyzed for mineral and potentially toxic elements (PTEs) through inductively coupled plasma optical emission spectrometry (ICP‒OES). Through deterministic and probabilistic risk assessment models, the daily intake of PTEs with allied health risks from consumption of rice were estimated for children and adults. The results of soil pH (< 8.5) and electrical conductivity (EC > 400 μs/cm), indicated slightly saline nature. The mean phosphorus concentration of 291.50 (mg/kg) in soil samples exceeded FAO/WHO permissible limits. The normalized variation matrix of soil pH with respect to Ni (0.05), Ca (0.05), EC (0.08), and Mg (0.09), indicated significant influence of pH on PTEs mobility. In rice grains, the mean concentrations (mg/kg) of Mg (463.81), Al (70.40), As (1.23), Cr (12.53), Cu (36.07), Fe (144.32), Mn (13.89), and Ni (1.60) exceeded FAO/WHO safety limits. The transfer factor >1 for K, Cu, P and Zn indicated bioavailability and transfer of these elements from soil to rice grains. Monte Carlo simulations of hazard index >1 for Cr, Zn, As, and Cu with certainties of 89.93% and 90.17%, indicated significant noncarcinogenic risks for children and adults from rice consumption. The total carcinogenic risk (TCR) for adults and children exceeded the USEPA acceptable limits of 1×10-6 to 1×10-4, respectively. The sensitivity analysis showed that the ingestion rate was a key risk factor. Arsenic (As) primarily influenced total cancer risk (TCR) in children, while chromium (Cr) significantly impacted adults. Deterministic cancer risk values slightly exceeded probabilistic values due to inherent uncertainties in deterministic analysis. Rice consumption poses health risks, mainly from exposure to Cr, Ni and As in the investigated area.

The high levels of heavy metal accumulation in cultivated rice from the Tajan river basin: Health and ecological risk assessment

Consumption of food crops contaminated with heavy metals (HMs) is a significant risk factor for human health and safety. We evaluated the health risks of HMs in contaminated food crops irrigated with surface water. Results showed there is a substantial buildup of HMs in rice, collected from the Tajan river basin, Iran. The transfer factor (TF) value for toxic elements Cd (3.6-12.4) and Pb (4.9-23.6) were significantly high and exceeded the permissible limits for crops set by WHO. The principal component analysis was used to analyze the relevance of different metals and identify the primary sources. The results showed that two factors dominated the metals variability (94.10% of total variance) that Cr, Fe, Cd, and Pb were dominated by PC1 whereas another factor charged Zn and Cu. The average total hazard quotient (THQ) values for Pb, Fe, Cr, and Cd were 13.8, 7.7, 5.5, and 1.5, respectively, that suggest a considerable risk to the health of regular rice consumers. The high hazard index (HI) value (29.2) demonstrated that the exposure concentration was very high compared to the effective threshold, and it may have potentially harmful implications for human health. To sum up, these results proved that rice from this basin could be a serious dietary source of Pb and Cd exposure to the consumer population.

Fractional distribution of thallium in paddy soil and its bioavailability to rice

To investigate the bioavailability of thallium (Tl) in soil and rice in a Tl-contaminated area in Guangdong, China, the topsoil and rice samples were collected from 24 sampling sites and analyzed. Moreover, a modified sequential extraction procedure was applied to determine the different Tl fractions in the soil. The mean pH value of the soil samples was 4.50. The total Tl concentration in the paddy soil was about 4-8 times higher than the Canadian guideline value (1mgkg^-1) for agricultural land uses. The mean ecological risk index of Tl was determined to be 483, indicating that potential hazard of the paddy soil was serious. The mean content of Tl in rice was 1.42mgkg^-1, which exceeded the German maximum permissible level (0.5mgkg^-1) of Tl in foods and feedstuffs by a factor of nearly 3. The hazard quotient value via rice intake was 57.6, indicating a high potential health risk to the local residents. The distribution of various Tl fractions followed the order of easily reducible fraction (40.3%) > acid exchangeable fraction (30.5%) > residual fraction (23.8%) > oxidizable fraction (5.4%). Correlation analyses showed that the easily reducible fraction correlates positively with the soil Fe and Mn contents, whereas the acid exchangeable fraction is significantly correlated with the S content. The soil pH was negatively correlated with the Tl content in both soil and rice. The Tl content in rice was more strongly correlated with the exchangeable fraction than the total Tl content in the soil. Overall, the bioavailability of Tl in more acidic soil is higher, and is strongly dependent on the speciation of Tl, especially the content of acid exchangeable fraction.