This study measured nine metals in 32 agricultural soil samples from the Liwa area of the UAE and found low overall pollution, but moderate cadmium contamination with a high ecological risk.
Authors
- Al-Taani, A. A., Nazzal, Y., Howari, F. M., Iqbal, J., Bou Orm, N., Xavier, C. M., Bărbulescu, A., Sharma, M., & Dumitriu, C.-S. , Toxics, 2021
What was studied
This study investigated the levels of heavy metals in agricultural soils of the Liwa area, a primary food-production region of the United Arab Emirates (UAE) in the Emirate of Abu Dhabi that has been used intensively for agriculture. Soils were analysed for manganese (Mn), zinc (Zn), chromium (Cr), nickel (Ni), copper (Cu), lead (Pb), cadmium (Cd), cobalt (Co) and arsenic (As) by ICP-OES. Contamination was evaluated with the enrichment factor, the geo-accumulation index (Igeo), contamination factors, the pollution load index (PLI) and the potential ecological risk index (PERI).
Who was studied
The study focused on agricultural soil, not on human or animal subjects. Thirty-two soil samples were collected from the upper 10 cm of farm soils in the Liwa area. No human health risk model was applied; the risk assessment concerned soil contamination and ecological risk.
Most important findings
| Critical Points | Details |
|---|---|
| Concentration Levels | Metal levels ranged from 220.02–311.21 mg/kg for Mn, 42.39–66.92 mg/kg for Zn, 43.43–71.55 mg/kg for Cr, 32.86–52.12 mg/kg for Ni, 10.29–21.70 mg/kg for Cu, 2.83–8.84 mg/kg for Pb, 0.46–0.69 mg/kg for Cd (mean 0.58 mg/kg) and 0.03–0.37 mg/kg for Co. Arsenic was low in all samples, averaging about 0.01 mg/kg. |
| Sources | Variation in metal content was linked to multiple sources, including agrochemicals, atmospheric dust carrying heavy metals, and traffic-related metals. |
| Enrichment | Enrichment factor analysis showed that Cd, Ni, Zn and Cr were highly enriched and could originate from non-crustal sources. |
| Pollution Indices | By the geo-accumulation index, soils were uncontaminated with Mn, Cr, Zn, Pb, Co, As and Cu, uncontaminated to moderately contaminated with Ni, and moderately contaminated with Cd. Contamination factors indicated low contamination except for Ni (moderate), and the average pollution load index indicated unpolluted to low pollution. |
| Ecological Risk | All metals posed a low ecological risk except cadmium, which showed a high ecological risk (mean single-metal risk index 173.63). |
Key Implications
Even in soils that are largely unpolluted overall, cadmium can stand out as the metal of ecological concern in intensively farmed land, with agrochemicals among its likely sources. Cadmium in agricultural soil matters for food safety because crops can take it up. For heavy metal testing programs such as Heavy Metal Tested and Certified (HMTC), the study supports paying particular attention to cadmium in produce grown in intensively farmed arid soils. The study measured soils only and did not measure metals in crops or estimate human exposure.
Citation
Al-Taani, A. A., Nazzal, Y., Howari, F. M., Iqbal, J., Bou Orm, N., Xavier, C. M., Bărbulescu, A., Sharma, M., & Dumitriu, C.-S. (2021). Contamination Assessment of Heavy Metals in Agricultural Soil, in the Liwa Area (UAE). Toxics, 9(3), 53. doi:10.3390/toxics9030053
Heavy metals are high-density elements that accumulate in the body and environment, disrupting biological processes. Lead, cadmium, arsenic, mercury, nickel, tin, aluminum, and chromium are of greatest concern due to persistence, bioaccumulation, and health risks, making them central to the HMTC program’s safety standards.
Lead is a neurotoxic heavy metal for which no safe blood lead level in children has been identified. It contaminates food, consumer goods and drinking water, and exposure is linked to cognitive deficits in children, adverse pregnancy outcomes such as preterm birth and low birth weight, and cardiovascular disease. HMTC’s rigorous lead testing applies ALARA principles to protect infants and consumers and to prepare brands for tightening regulations.
Cadmium is a persistent heavy metal that accumulates in kidneys and bones. Dietary sources include cereals, cocoa, shellfish and vegetables, while smokers and industrial workers receive higher exposures. Studies link cadmium to kidney dysfunction, bone fractures and cancer.
Nickel is a widely used transition metal found in alloys, batteries, and consumer products that also contaminates food and water. Oral nickel can trigger eczema flare-ups in people already sensitised to nickel, and EFSA has set a tolerable daily intake of 13 μg/kg body weight based on developmental effects seen in animal studies. EFSA found that high-consuming toddlers and other children generally exceed this intake. Nickel has been measured in placental and umbilical cord blood, and its links to pregnancy outcomes are still being studied, which is why HMTC applies stricter limits to protect vulnerable populations.