Cadmium isotope fractionation in the soil - cacao systems of Ecuador: a pilot field study.
Cadmium isotope fractionation in the soil - cacao systems of Ecuador: a pilot field study.
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DOI：
10.1039/c9ra05516a
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发表时间：
2019-10-18
期刊：
影响因子：
3.9
通讯作者：
Maurice, Laurence
中科院分区：
文献类型：
--
作者：
Barraza, Fiorella;Moore, Rebekah E. T.;Rehkamper, Mark;Schreck, Eva;Lefeuvre, Gregoire;Kreissig, Katharina;Coles, Barry J.;Maurice, Laurence
可可豆的镉含量往往很高，这是拉丁美洲生产商的一个严重问题，因为欧盟在2019年对可可产品实施了更严格的镉限制。这是第一次调查采用耦合镉同位素和浓度测量研究土壤可可系统。分析了29个样品的土壤，土壤改良剂和可可树器官有机农场在厄瓜多尔收获三个不同的可可品种。大多数0-80 cm深度的土壤具有非常相似的δ114/110 Cd，约为−0.1‰至0‰。两个0- 5cm表层土壤Cd含量较高，δ114/110 Cd> 0.2%，表明土壤Cd可能来自于作为有机肥料的枯枝落叶。虽然可可叶，豆荚和豆类普遍富集镉相对于土壤有不同的镉同位素的签名。叶片和荚果比土壤重，其Δ114/110 Cd值为0.22 ± 0.07‰ ~ 0.41 ± 0.09‰。相比之下，数据揭示了Δ114/110 Cd豆叶的差异，这可能与不同的可可品种有关。具体而言，两个农场的Nacional可可豆的Δ114/110 Cd豆叶值为−0.34‰至−0.40‰，而第三个农场的CCN-51杂交可可豆在误差范围内没有分离（−0.08 ± 0.13‰）。因此，进一步的工作，以调查镉同位素是否确实是有用的土壤中的镉富集的来源，并告知遗传努力，以减少可可的镉负担。可可中的镉同位素组成似乎是特定的品种，而土壤中的镉可能是由于树木凋落物回收。
The often high Cd concentrations of cacao beans are a serious concern for producers in Latin America due to the implementation of stricter Cd limits for cocoa products by the European Union in 2019. This is the first investigation to employ coupled Cd isotope and concentration measurements to study soil – cacao systems. Analyses were carried out for 29 samples of soils, soil amendments and cacao tree organs from organic farms in Ecuador that harvest three distinct cacao cultivars. The majority of soils from 0–80 cm depth have very similar δ114/110Cd of about −0.1‰ to 0‰. Two 0–5 cm topsoils, however, have high Cd concentrations coupled with heavy Cd isotope compositions of δ114/110Cd ≈ 0.2%, possibly indicating Cd additions from the tree litter used as organic fertilizer. Whilst cacao leaves, pods and beans are ubiquitously enriched in Cd relative to soils there are distinct Cd isotope signatures. The leaves and pods are isotopically heavier than the soils, with similar Δ114/110Cdleaf–soil values of 0.22 ± 0.07‰ to 0.41 ± 0.09‰. In contrast, the data reveal differences in Δ114/110Cdbean–leaf that may be linked to distinct cacao cultivars. In detail, Δ114/110Cdbean–leaf values of −0.34‰ to −0.40‰ were obtained for Nacional cacao from two farms, whilst CCN-51 hybrid cacao from a third farm showed no fractionation within error (−0.08 ± 0.13‰). As such, further work to investigate whether Cd isotopes are indeed useful for tracing sources of Cd enrichments in soils and to inform genetic efforts to reduce the Cd burden of cocoa is indicated. Cd isotope composition in cacao seems to be cultivar-specific whereas Cd in soil is probably due to tree litter recycling.
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