No.3 - Transferência do urânio no sistema água-solo-planta (Lactuca sativa L.) na área mineira da Cunha Baixa

Orquídia Neves, Maria Manuela Abreu, Elsa M. Vicente


The water of private wells located nearby Cunha Baixa mine site (Portugal, Mangualde) has been used for the last two decades as source of irrigation for vegetable-garden productions. High levels of uranium in irrigation water have raised health concerns expressed by homeowners of the most affected wells. Uranium could be accumulated in soils or may gradually pass into the edible parts of the vegetables, posing health risks to humans. This study was carried out on lettuce (Lactuca sativa L.) growing in two soils (SCB1 and SCB2) located in an agricultural area nearby the abandoned uranium mine, in order to evaluate uranium uptake and distribution in the edible and non-edible plant parts. Lettuce is a usual vegetable of the inhabitants diet during the year (spring to autumn). Uranium concentration was determined in lettuce leaves and roots. Composite soil samples collected before and after lettuce growth period, were analysed for total and bioavailable uranium after acid digestion and ammonium acetate extraction, respectively. The water used for irrigation (uranium contaminated and non-contaminated) and sampled during the growth period was also analysed. Lettuce roots accumulate more uranium than leaves (mean uranium concentration ranged from 1.07 to 4.6 mg/kg dry weigh and from 0.42 to 2.13 mg/kg dry weight, respectively). The highest uranium concentration in lettuce plants was detected in the soil that had higher total and available uranium concentration (SCB2: 95.9±16.0 and 14.69±3.40 mg/kg, respectively). However, there are no significant differences on lettuce uranium uptake for plants growing in the same soil and irrigated with different uranium water quality (mean uranium concentration of 19±1 µg/L and 1064±76 µg/L). The soil-plant coefficient transfer (CTS) and the water-plant coefficient transfer (CTA) calculated for leaves and root tissues, using, respectively, the uranium soil available fraction and the uranium concentration in irrigation water, showed that plants moderately absorbed uranium from soil and presented some tolerance to high uranium water content that not limited its development. These results may indicate some health risk by lettuce ingestion if together with others enriched uranium foodstuff the tolerable diary intake guideline recommended by World Health Organisation (0.6 µg/kg bodyweight) will be exceeded. These field experiments are important as data on uranium levels in vegetables food grown in soils around Portuguese uranium mines was non-existent and it is priority to make an assessment of the health risks to the local residents.

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Uranium, lettuce, uptake, transfer coefficient, Cunha Baixa

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