Heavy Metal Contamination in Food Crops in Lebanon: comparative assessment of pollution using atomic absorption and hyperspectral imaging

Abstract

Heavy metals (HMs) contamination in soil and food crops constitutes a major threat to human health. In Lebanon, few studies have assessed the levels of heavy metal contamination in food crops and were limited to specific geographic areas. In addition, the use of hyperspectral imaging (HSI) for the detection of HMs contamination in agricultural soils and crops in Lebanon is still not tested. This study aims at conducting a nationwide assessment of HM contamination in leafy vegetables across major agricultural areas in Lebanon and evaluating the use of HSI as an emerging and reliable technique for the detection of HM pollution in food crops. A total of 48 vegetable samples corresponding to 16 different vegetation species were collected across major agricultural areas in Lebanon covering all country’s governorates. Levels of zinc (Zn), copper (Cu), chromium (Cr), cadmium (Cd), nickel (Ni), and lead (Pb) were measured in the collected vegetables using atomic absorption spectrophotometry (AAS). Subsequently, HSI was performed on dried vegetable samples, and a regression model was developed with SPSS (Statistical Package for the Social Sciences) using atomic absorption data and wavelength reflectance as dependent and independent variables, respectively. The findings showed significant contamination of the tested vegetables with Cr (15 ± 10 mg/kg), Cd (0.38 ± 0.3 mg/kg), and Pb (0.72 ± 0.5 mg/kg) exceeding the WHO/FAO allowed thresholds in food crops in more than 75% of the tested samples. The source of this contamination was associated with the utilization of polluted water for irrigation purposes and the indiscriminate use of fertilizers. In the case of zinc, moderate contamination averaging 86.5 ± 60 mg/kg was reported and exceeded WHO/FAO limits in 37% of the tested samples. Copper concentrations averaged 37.7 ± 20 mg/kg and were below permissible limits in all tested vegetables except in okra, which showed copper concentrations slightly exceeding the WHO/FAO limits. In addition, nickel concentrations were below permissible limits in all tested vegetables with an average measured value of 1.05 ± 1mg/kg. The calculated health risk index (HRI) was lower than 1 for all metals demonstrating that people are not subjected to a significant potential health risk from the intake of a single metal consumed in any of the tested vegetables. However, it is essential to note that evaluating accumulation risk, especially for heavy metals, requires a comprehensive approach, considering complex pollutant interactions, cumulative health effects, diverse exposure routes, and both short- and long-term health consequences, for a thorough understanding and management of risks from environmental contaminant accumulation. Hyperspectral imaging was not successful in detecting and quantifying HMs pollution in food crops, namely due to the lack of a critical spectral range within the used equipment able to detect chlorophyll bands. In addition, the relatively low heavy metal concentrations measured in the tested crops, which are restricted to a narrow contamination range, caused the data to be unpredictable by the imaging technique. The findings from this study highlight the occurrence of heavy metals in frequently consumed vegetables by the Lebanese population and the need for continuous monitoring, effective waste disposal, adequate use of fertilizers, and the use of alternative non-polluted irrigation sources to safeguard the integrity of consumed food items. The negative outcomes from the HSI analysis provide valuable insights for future investigations. Expanding the scope of the study to encompass a wider range of HM concentrations and plant species would permit drawing solid conclusions on the use of HSI in the detection of HMs in vegetables and enhance the applicability of the results.