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.