Insights into the Environmental Dynamics of Legacy and Current-use Pesticides in the Tropics through Multimedia Models
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Date
2017
Publication Type
Doctoral Thesis
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Abstract
A large divide in environmental science exists between the developed (“Northern”) and developing (“Southern”) countries. The latter, mainly located in tropical and subtropical regions, have been neglected as environmental research subjects and have only been marginally involved in generating knowledge and in setting research priorities. Only approximately 6% of all papers published in the most-cited nine environmental science journals from 1993-2003 focused in tropical and subtropical ecosystems. Yet, tropical ecosystems account for 52% of the Earth’s surface, are critical to the global carbon and hydrogeological cycles, harbor most of the world’s biodiversity, and are a source of valuable renewable and non-renewable resources. This North-South disparity precludes the contribution of research from the South to national and global environmental governance, and limits the visibility of issues that concern the South in the global policy agenda. The Northern bias also results in a narrow, incomplete understanding of environmental systems and biased global environmental assessments.
Within this North-South divide, significant knowledge gaps exist in the Tropics regarding the use patterns, properties, fate, transport and effects of pesticides, some of which are even classified as persistent organic pollutants. In the Tropics, pesticides are mainly used for the control of vector-borne diseases endemic to these areas, and as the main method of pest control in conventional agriculture. Pesticide use intensity and frequency is higher in the Tropics as the climates favor increased pest pressure and year-round crop growth. Pesticide use is expected to increase as tropical agricultural lands expand to satisfy the growing worldwide food demand. Several studies in the Tropics have detected pesticide residues in environmental matrices, biota, and humans in non-target sites. However, most of these studies are snapshots that often do not take into account temporal and spatial variability, resulting in scattered insights on pesticide behavior and limiting the ability to assess exposure.
This thesis seeks to contribute to narrowing the North-South knowledge divide by coupling monitoring data with dynamic multimedia models to investigate the environmental fate and transport of pesticides used for health-care and agricultural purposes in the Tropics. The research presented herein capitalizes on the existing knowledge base in the South on chemical behavior, including grey literature and the field experience of Southern collaborators, and builds up on it through suitable approaches developed in the North, namely multimedia models.
The first case study presented in this thesis addresses the cycling of a legacy pesticide used for malaria vector control in a remote community in the Brazilian Amazon, which relies on local sources of water and food. In Brazil, DDT was officially used for indoor residual spraying (IRS) against malaria and leishmaniasis from the 1960s up to a ban in 1998. In the community of Lake Puruzinho, DDT levels measured in human breastmilk in 2004 were significantly higher than WHO recommendations, and than those measured in neighboring communities with a similar history of DDT use for IRS. To investigate the fate of DDT and its transformation products in Puruzinho and to assess environmental exposure, soil and sediment measurements were conducted from 2005-2014 and a dynamic multimedia floodplain model was developed. The daily-resolved model takes into account the variable lake water levels, rainfall, and changes in emissions patterns based on legislation. Model results and measurements showed that DDT and its metabolites, DDE, and DDD (collectively, DDX), accumulate mainly in upland soils and sediments. Measurements show significant increases of DDX levels in the soil from 2005-2014 in association with decreasing DDE/DDT ratios, which disagree with model results assuming that DDT use ceases after 1998. This comparison and the availability of DDT stockpiles in the region suggest that post-ban DDT emissions are very likely, so two additional scenarios were tested: one assuming DDT use for IRS after a malaria upsurge, and another assuming its use against leishmaniasis and termites. Under both re-emissions scenarios, model results for DDX concentrations and DDE/DDT in soils agree with measurements, while those in sediments were between the two re-emissions scenarios. The model-measurement agreement in soils suggests that the fractions of formation and half-lives used to describe degradation in soil were adequate in the model. Further sediment measurements and research to refine highly uncertain parameters associated with degradation and partitioning in sediments are required to improve the model’s representation of DDX cycling.
The second case study addresses the fate and transport of pesticides currently used for banana and pineapple cultivation in the Caño Azul River drainage basin in Costa Rica, the world’s 3rd largest banana producer. Pesticide monitoring programs in Europe and the United States, the main importers of Costa Rican bananas, show that residues in bananas are not of concern to consumer health. However, in banana-producing regions of Costa Rica, located mainly on the Caribbean Coast, pesticides have repeatedly been detected in rivers, canals, and wetlands, at levels associated with negative acute and chronic effects on aquatic organisms. Pesticide concentrations above USEPA recommendations for chronic exposure have also been detected in children and pregnant women living in the vicinity of banana plantations. Most studies on pesticide residues in the Costa Rican environment are scattered in time and space, which prevents adequate exposure assessments given the variable pesticide use patterns and characteristic pesticide pulses observed in surface waters. To capture these dynamics, a multimedia model was developed for the Caño Azul River drainage basin, which is influenced by two banana plantations and one pineapple plantation, and where pesticide measurements in water and air were available for model validation. The model estimates concentrations of three representative chemicals—the herbicide diuron, the nematicide ethoprofos, and the fungicide epoxiconazole—in water, air, soil, sediments, and banana plants. Model results show highly variable concentrations in water, with peaks that are driven by rainfall and emissions and that sometimes exceed thresholds for ecosystem health. Conversely, concentrations in the fruit remain below the EU and US maximum residue limits. Model improvements to better estimate pesticide concentrations include fine-tuning sediment dynamics and incorporating the impact of adjuvants on the properties of active ingredients.
The models developed here have a flexible design, so additional processes and compartments can be incorporated as new insights are gained into pesticide partitioning, degradation, and mass transfer processes in the Tropics, perhaps in response to the research calls within this thesis. Upon further validation, the models can be used to evaluate the environmental fate of pesticides proposed as alternatives and of problematic degradation products of existing chemicals. They can also be used to assess environmental exposure to pesticides that have not been measured in the environment due to analytical limitations, yet are widely used, such as fungicide mancozeb in banana cultivation. It is important to note that even though multimedia models are valuable decision support tools for identifying opportunities to reduce pesticide exposure and transfer to non-target sites, they should complement pesticide safe handling and use practices suitable for the Tropics, and strategies to minimize pesticide use such as integrated pest management.
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Examiner : Hungerbühler, Konrad
Examiner : Ng, Carla
Examiner : Bucheli, Thomas
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ETH Zurich
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Subject
Environment; environmental science; environmental chemistry; Tropics; Pesticide
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03402 - Hungerbühler, Konrad (emeritus) / Hungerbühler, Konrad (emeritus)