Understanding Cadmium Uptake by Cocoa Plants via Cd Isotope Analyses

Lead Research Organisation: Imperial College London
Department Name: Earth Science and Engineering

Abstract

Cadmium (Cd) is a trace metal that is highly toxic even at low concentrations. The relatively high Cd abundances often found in cocoa are a serious problem for the cocoa producers of developing nations, as the European Union plans to implement strict new upper limits for Cd in cocoa products in 2019. This development has recently spurred research into the causes of Cd enrichment in cocoa. Such work has mainly focused on the impact of external factors, such as soil type, pH and cultivation practices, on the Cd content of cocoa but until now, these investigations have failed to provide conclusive results. Hence, it has been suggested that Cd accumulation may vary across different cocoa varieties but this possible link has yet to be investigated.

The current project constitutes collaborative research by Prof M Rehkamper, an isotope geochemist at Imperial College London, and Prof J Dunwell, a plant physiologist at the University of Reading. Previous work of Rehkamper has shown that coupled Cd concentration and stable isotope analyses, initially developed for planetary science research, can provide unique insights into Cd uptake and translocation by plants. Furthermore, a 2015 pilot study of Rehkamper and Dunwell revealed that such analyses are also promising for cocoa.

In the current 6-month project, the results of the 2015 pilot experiment will be verified, to ensure that coupled Cd concentration and isotope data indeed provide a reliable measure for Cd uptake by and translocation within plants. Furthermore, a suite of different cocoa varieties will be analysed to characterise the overall variability of Cd uptake and accumulation amongst different types of this plant. Together, the results will enable an initial identification of cocoa varieties that are particularly suitable for cultivation because they feature minimal Cd accumulation in beans, due to low uptake of Cd by the plant and reduced transport from the roots to the fruit.

As such, the results of this study can make an important contribution to the development of sustainable methods for the production of cocoa beans with safe levels of Cd, thereby ensuring a reliable source of income for cocoa producers in developing nations and boosting the economies of rural communities.

Planned Impact

This study will provide an improved understanding of cadmium (Cd) accumulation in cocoa and an initial assessment of the variability of Cd uptake amongst different cocoa varieties. As such, our results are of direct societal and economic relevance. In particular, a better understanding of how different cocoa varieties and cultivation practices impact the Cd content of cocoa means that farmers can adopt practices, which produce market-acceptable cocoa with safe levels of Cd, thereby sustaining local economies in rural communities. In addition, our work also helps to secure a reliable supply of cocoa for the chocolate industry (including local producers in developing countries) and is ultimately of benefit to all consumers of cocoa products.

Given the possible societal and economic impact of our work, relevant stakeholder will be briefed directly on the results. Engagement of cocoa stakeholders will thereby be developed through the existing links of Project Partner Dunwell. In fact, our 2015 pilot study was initiated in response to requests to Dunwell from cocoa growers and industry to identify new solutions for the problem of Cd accumulation in cocoa. Notably, the results of our pilot investigation were already communicated to the stakeholders in January 2016, and they subsequently agreed to release resources from an existing grant to fund the UR research component of the present study.

Direct briefing of stakeholders on the findings of this project and their implications for cultivation practices to reduce Cd accumulation is, therefore, of key importance. Of particular significance in this context are Dunwell's close links to national cocoa research institutes, especially in South & Central America, where the problem of Cd accumulation appears to be most severe and the institutes are already involved in studies to reduce Cd accumulation in cocoa.

By providing our findings on suitable genotypes to such research centres, including CATIE in Costa Rica, INIAP in Ecuador, and CORPOICA in Columbia (and others), they can be incorporated into on-going breeding programs, which in turn routinely support and supply local farmers. In addition, existing contacts with industry, such as local chocolate producers (e.g., Casa Luker, Colombia) and cocoa exporters (e.g., ANECACAO), larger estates (e.g., Las Canas, Ecuador), as well as governmental (e.g., ICCO) and trade associations (e.g., ABICAB Brazil) will be utilized, to raise awareness for our work and support adoption of revised practices.

Ultimately, our research is poised to support the rural cocoa producers of developing nations, by aiding the identification of cocoa genotypes and/or cultivation practises that enable sustainable production of cocoa beans with low Cd contents. The current project, however, cannot provide a comprehensive response to this challenge, because only a small number of genotypes (in comparison to the known genetic diversity) can be screened. Hence, we intend to carry out a comprehensive follow-up investigation that involves coupled Cd concentration and isotope analyses for a much larger suite of genotypes and samples. Funding for such a follow-up study can be sought from a number of sources. In particular, we envision a Global Challenge Research Fund application because such follow-up work is ODA eligible, as it focuses on the needs of developing nations and is of particular significance to poorer communities. In addition, we will utilize Dunwell's links with cocoa stakeholders to discuss and encourage further funding for a follow-up investigation (particularly from industry) and consider the feasibility of RCUK research grant applications.

Publications

10 25 50
 
Description Cocoa producers in many developing countries are struggling to meet the upper limits for the cadmium (Cd) contents of cocoa that the European Union enacted in January 2019. The scale of the 'Cd problem' is significant, as it affects numerous countries in Latin America and southeast Asia (e.g., Colombia, Ecuador, Honduras, Indonesia, Peru, Trinidad & Tobago, Venezuela) to a worrisome extent, and it has thus alarmed various stakeholders, including cacao farmers, governments and the chocolate industry. Notably, more than 80% of cacao is harvested on family-owned farms, such that it provides the primary source of income for more than 5 million farmers and affords livelihoods for about 40 million rural workers and their families. In Ecuador, for example, 90% of cacao beans are harvested by about 100,000 smallholders and nearly 50% of farms produce beans with Cd contents that exceed the suggested threshold. Hence, any limitation of cocoa exports will have an enormous impact on the rural populations of many developing countries.

Our research has shown that certain agricultural practices have an important impact on the Cd uptake of cacao plants. This finding can contribute to the development of sustainable cacao cultivation practices, which enable production of cocoa with safe levels of Cd. In fact, revised cultivation practices that take into account our findings are currently being tested in Ecuador.

Further work has demonstrated that cacao genotypes differ widely in the extent to which they take up and store Cd within the plant. In addition, we have started to identify the individual cacao transporter proteins, which are responsible for the efficient uptake and sequestration of Cd by cacao. These findings are important to inform ongoing breeding and genetic efforts that aim to address the Cd problem of cacao, to ensure a reliable source of income for cacao farmers and their families in affected developing countries.
Exploitation Route All results of the project will be written up and published, such that they are widely available. One article is already published and a second manuscript is in review.

An Ecuadorian project partner has briefed relevant official from the government and farmer cooperatives on the results of our work. As a consequence of our work (and further studies by other researchers), some suggested changes to cultivation practices are already being trialed in the field.

With support from follow-on funds that are available from a Research England GCRF block grant to Imperial College London my team is currently:

- investigating whether the adoption of suggested changes in agronomic practices are having a positive impact on the Cd contents of cacao beans

- conducting further analyses of transgenic yeast and plants to identify additional transporter proteins that play a key role in the uptake and sequestration of Cd by cacao plants. A good understanding of relevant Cd transporter proteins is necessary to direct breeding and genetic efforts, which are underway to address the Cd problem of cacao and alleviate negative impacts for the rural populations of numerous developing countries.
Sectors Agriculture, Food and Drink,Environment

 
Description Cocoa producers in many developing countries are struggling to meet the upper limits for the cadmium (Cd) contents of cocoa that the European Union enacted in January 2019. The scale of the 'Cd problem' is significant, as it affects numerous countries in Latin America and southeast Asia (e.g., Colombia, Ecuador, Honduras, Indonesia, Peru, Trinidad & Tobago, Venezuela) to a worrisome extent, and it has thus alarmed various stakeholders, including cacao farmers, governments and the chocolate industry. Notably, more than 80% of cacao is harvested on family-owned farms, such that it provides the primary source of income for more than 5 million farmers and affords livelihoods for about 40 million rural workers and their families. In Ecuador, for example, 90% of cacao beans are harvested by about 100,000 smallholders and nearly 50% of farms produce beans with Cd contents that exceed the suggested threshold. Hence, any limitation of cocoa exports will have an enormous impact on the rural populations of many developing countries. Our research has shown that certain agricultural practices have an important impact on the Cd uptake of cacao plants. This finding can contribute to the development of sustainable cacao cultivation methods, which enable production of cocoa with safe levels of Cd. In fact, revised cultivation practises that take into account our findings are currently being tested in Ecuador and we will investigate the success of the measures in a follow-on study (that encompasses a field campaign for sampling as well as subsequent Cd analyses), which is currently underway. If the measures are successful, they can be implemented in other countries where cacao is cultured and similar problems with high Cd levels in cocoa beans are prevalent (e.g., Colombia, Honduras, Indonesia, Peru, Trinidad & Tobago, Venezuela). In addition, we recently completed a pilot study, which demonstrated large systematic differences in the uptake of Cd by different cacao genotypes. Further experiments with transgenic yeast identified two metal transporter proteins, which play a key role in the uptake and sequestration of Cd in cacao plants. The results of these studies have been submitted for publication and the manuscript is currently in review. In addition, further investigations of additional metal transporter proteins are underway with support from follow-on funding. Such studies are of key importance because they can underpin breeding and genetic efforts to reduce the Cd burden of cacao beans. Gender Equality Statement The aim of our research is ensure that the new EU regulations on the maximum Cd contents of cocoa and cocoa products have no negative economic impact on farming communities in regions that currently produce cacao beans with problematic Cd levels. This will be achieved by identifying agronomic and genetic solutions to the 'Cd problem', which can be implemented by cacao farmers in the field. Considering this, a positive research outcome would be to maintain the current economic status of the cacao farmers and rural populations of affected regions. Such a positive outcome would imply that the research has little, and certainly no negative, impact on gender relations. Furthermore, warding off possible negative economic consequences of the 'Cd problem' will provide benefits to all members of affected farming communities, regardless of gender. Given that better economic conditions are generally conducive for advancing gender equality, our research is unlikely to generate negative consequences for gender relations.
First Year Of Impact 2018
Sector Environment
Impact Types Societal,Economic

 
Description Cacao cultivation practices in Ecuador
Geographic Reach Local/Municipal/Regional 
Policy Influence Type Influenced training of practitioners or researchers
Impact The results of our initial analyses of soils and cacao plants from Ecuador suggest that certain cultivation practices may contribute to high Cd levels in cacao beans. Based on these results (and similar findings of other workers), some farms In Ecuador are trialing revised cultivation practices. Using follow-on funding, we will sample soils and cacao plants at such farms to evaluate whether the revised cultivation practices are having a positive impact on the Cd contents of cacao beans.
 
Description Identification of cadmium sources in cacao soils by isotopic profiling
Amount £50,262 (GBP)
Organisation Mars Wrigley Confectionery UK Ltd 
Sector Private
Country United Kingdom
Start 12/2017 
End 12/2019
 
Description Reducing cadmium enrichments in cacao beans - New constraints from Cd isotope analyses (from Research England GCRF grant to Imperial College)
Amount £54,782 (GBP)
Organisation Imperial College London 
Sector Academic/University
Country United Kingdom
Start 01/2020 
End 07/2020
 
Title Coupled Cd isotope and concentration analyses of soil-cacao systems 
Description Our project represents the fist time coupled Cd stable isotope and concentration analyses are being used to study the uptake of Cd from soils into cacao plants. 
Type Of Material Biological samples 
Year Produced 2017 
Provided To Others? Yes  
Impact The new methodology provides novel constraints to study the uptake and sequestration of Cd by cacao and other plants. As such, it is uniquely suitable for developing mitigation measures to avoid high Cd contents in cacao and other crops (e.g., wheat, rice). 
 
Description Impact of agricultural practises on Cd uptake of cacao (with partners in Colombia) 
Organisation University of Antonio Narino
Country Colombia 
Sector Academic/University 
PI Contribution I played a leading role in the preparation of research proposals to (i) investigate the impact of agricultural practices on Cd uptake of cacao and (ii) develop suitable mitigation measures. Two proposals were to fund field campaigns in Colombia for sample collection as well as subsequent Cd isotope and concentration analyses for soil and cacao samples. The novel data acquired in these analyses would allow an improved assessment of the impact of various cultivation locations (particularly different soils) and practices on the Cd contents of cacao beans. A further proposal requests funds to host a workshop on the 'Cd in cacao problem' in Bogota, Colombia. This workshop would bring together scientists from Latin America, the US and Europe to discuss the current understanding of Cd uptake by cacao and identify promising mitigation measures.
Collaborator Contribution Contribution to the preparation of joint research proposals.
Impact No outcomes yet as two research proposals were not funded. A third proposal is currently still in evaluation.
Start Year 2019
 
Description Impact of agricultural practises on Cd uptake of cacao (with partners in Ecuador) 
Organisation Institute of Development Research (IRD)
Country France 
Sector Academic/University 
PI Contribution Coupled Cd isotope and concentration analyses of the soil and cacao samples at Imperial College London. Joint interpretation of results obtained in the analyses with research partners. Joint dissemination of the results in journal articles and at conferences.
Collaborator Contribution Collection of soil and cacao samples at various locations in Ecuador. Basic characterisation of the soils (soil type, pH, Corg content). Transport of the samples to Imperial College. Joint interpretation of results obtained in the analyses. Joint dissemination of the results in journal articles and at conferences. Dissemination of the results and implications of the findings for improved cultivation of cacao (with lower Cd contents) to relevant bodies in Ecuador (government official responsible for agricultural practices, farmer cooperatives).
Impact A suite of about 40 samples from soil-cacao systems in Ecuador were collected and analysed. Following joint interpretation of the data, the results and interpretations were written up and the manuscript was published in 2019. A further joint project with field campaign in Ecuador and subsequent analyses at Imperial College is currently underway with follow-on funding. The collaboration is multi-disciplinary: The IRD / University Andina Simon Bolivar researchers are environmental scientists with the expertise that is needed (i) to carry out the field work for samples collection and (ii) for data interpretation My Imperial College team has the facilities and instrumentation that are required for the coupled Cd isotope and concentration analyses of the samples. Our input is also essential for rigorous data interpretation.
Start Year 2018
 
Description Impact of agricultural practises on Cd uptake of cacao (with partners in Ecuador) 
Organisation Simon Bolivar Andean University
Country Bolivia, Plurinational State of 
Sector Academic/University 
PI Contribution Coupled Cd isotope and concentration analyses of the soil and cacao samples at Imperial College London. Joint interpretation of results obtained in the analyses with research partners. Joint dissemination of the results in journal articles and at conferences.
Collaborator Contribution Collection of soil and cacao samples at various locations in Ecuador. Basic characterisation of the soils (soil type, pH, Corg content). Transport of the samples to Imperial College. Joint interpretation of results obtained in the analyses. Joint dissemination of the results in journal articles and at conferences. Dissemination of the results and implications of the findings for improved cultivation of cacao (with lower Cd contents) to relevant bodies in Ecuador (government official responsible for agricultural practices, farmer cooperatives).
Impact A suite of about 40 samples from soil-cacao systems in Ecuador were collected and analysed. Following joint interpretation of the data, the results and interpretations were written up and the manuscript was published in 2019. A further joint project with field campaign in Ecuador and subsequent analyses at Imperial College is currently underway with follow-on funding. The collaboration is multi-disciplinary: The IRD / University Andina Simon Bolivar researchers are environmental scientists with the expertise that is needed (i) to carry out the field work for samples collection and (ii) for data interpretation My Imperial College team has the facilities and instrumentation that are required for the coupled Cd isotope and concentration analyses of the samples. Our input is also essential for rigorous data interpretation.
Start Year 2018
 
Description Laboratory investigations into the Cd uptake of cacao (with U Reading) 
Organisation University of Reading
Country United Kingdom 
Sector Academic/University 
PI Contribution Joint design of experiments (i) to investigate whether and how different cacao genotypes differ in Cd uptake characteristics and (ii) with transgenic yeast to identify the metal transporter proteins that are responsible in cacao for the uptake and accumulation of Cd. The cacao plant / transgenic yeast samples cultivated in Reading were analysed in our laboratory at Imperial College London. The results were jointly interpreted and written up with the research partner. The manuscript was submitted for publication and is currently in review. Both researchers from Reading and Imperial College are presenting the results at conferences.
Collaborator Contribution Joint design of experiments (see above). Experiments conducted by research partner in their facilities: (i) cultivated different cacao genotypes under controlled conditions to investigate Cd uptake (ii) cultivated transgenic yeast to investigate impact of different metal transporter proteins on Cd uptake Joint interpretation of results and preparation / submission of a manuscript. Joint dissemination of results at conferences.
Impact Analyses of cacao and transgenic yeast samples cultivated at Reading have been completed at Imperial. Joint interpretation of results and preparation / submission of a manuscript is completed. We are currently awaiting the outcome of the peer review process. Further experiments with transgenic organisms to investigate the role of specific metal transporters in the Cd uptake of cacao are in progress with follow-on research funding. The collaboration is highly multi-disciplinary: - Researchers at Reading have the biological / genetic expertise and facilities to cultivate different cacao genotypes and prepare relevant transgenic yeast strains - My team at Imperial College has the analytical expertise to carry out the coupled Cd isotope and concentration analyses of the samples - The combined expertise of the Reading and Imperial College groups is required for the interpretation of the results
Start Year 2018