Melissa Marchese

Melissa Marchese taking feather samples with boat driver and field assistant, Pancho.
Upon my return to Duke [after a summer of fieldwork], we spent two semesters discussing and presenting our findings. I realized that a myriad of impactful questions in fields such as ecology, global health and policy remain unanswered. I decided to continue my research in this region by pursuing a senior thesis.


Environmental Sciences ’21

Project Team

My Senior Thesis Fieldwork Experience

One year ago, my Bass Connections group and I were wrapping up a successful summer of fieldwork in the Peruvian Amazon. Our eight-week ecological journey took us through the rainforest by car, boat, a four-wheel drive and on foot in an effort to better understand the fate of mercury in this particular environment. Following this first trip with Bass, I felt a strong connection to the region – its natural beauty, kind people and amazing food. Upon my return to Duke, we spent two semesters discussing and presenting our findings. I realized that a myriad of impactful questions in fields such as ecology, global health and policy remain unanswered. I decided to continue my research in this region by pursuing a senior thesis. Now, I write once again from Madre de Dios, Peru, with some new reflections after another summer of fieldwork.

Some Background on My Project

The basis for my research here, and that of several Bass Connections projects, lies in one enigmatic element – number 80 – mercury. The people of Madre de Dios face disproportionately high exposure to this neurotoxin as a result of its widespread use in local artisanal and small-scale gold mining practices. Miners use elemental mercury (quicksilver) to extract gold from river sediment because of its strong ability to bind the precious metal and form an amalgam. Later, the mercury ends up as mine tailings or vaporized to isolate the gold in an amalgam-burning step. It then takes on a gaseous form and enters the atmospheric cycle, by which it is eventually deposited onto the landscape. The inorganic mercury can then be methylated by microbes in anaerobic settings, biomagnified in organisms and consumed by humans. However, every source of mercury to humans is not well known, and the associated risks can be combated through a better understanding of environmental and dietary exposure pathways.

Last year, during the data collection and analyses for our Bass Connections project, I became interested in unique human exposure routes and began researching the mercury content of various locally grown crops. I found this work to be the perfect nexus between my interests in human health and ecology. Thus, to continue studying dietary mercury sources, I am expanding my research to other foodstuffs. While most studies in the region have focused on mercury content in fish, other foods may also contain the toxin. Based on studies from Africa, Asia and Europe, it is very possible that chicken, a major regional protein source, is another source of mercury for people.

My mentor Jackie (an Ecology Ph.D. candidate) and I walking through the mining town to collect chickens. Credit: Fernanda Machicao.
Walking through the mining town to collect chickens with my mentor Jackie, an Ecology Ph.D. candidate (at left) (Photo: Fernanda Machicao)

Walking around purchasing chickens is not what you might expect from an environmental science major doing fieldwork in a biodiversity hotspot. It’s not the first thing I would picture myself doing after collecting soil, water and plant material last year. However, after living and dining in these communities where backyard chicken populations are probably as high as human ones, this One Health approach to environmental studies really excited me.

Collecting Data: What and Why

Through my research, I am exploring chickens’ mercury content and the factors that affect it. I collected meat, eggs and feathers from mining towns (high mercury contamination) and non-mining towns (low contamination) in Madre de Dios. I will then analyze different cuts of the chicken for total mercury (all forms) and methyl mercury (the form highly toxic if ingested) to determine its distribution in tissues consumed by people. Because of how organisms process mercury, different organs and tissues may have higher levels than others. To further understand the determinants of mercury accumulation, I will analyze feathers for stable isotopes to see a free-range chicken’s place on the food chain and how that affects its mercury levels. Analyzing carbon and nitrogen isotopes will show what the chickens are eating (e.g., corn only, meat from table scraps, plants, bugs) and could help explain mercury trends.

Taking feather samples (and representing Duke!) with our awesome boat driver and field assistant, Pancho. Credit: Fernanda Machicao.
Taking feather samples (and representing Duke!) with our awesome boat driver and field assistant, Pancho (Photo: Fernanda Machicao)

Finally, I will estimate human mercury intake from eating local chickens. With these data, I can determine if eating chicken from mining or non-mining areas poses an exposure risk, how chickens’ diets affect that risk and if this specific bird species is accumulating significant quantities of mercury or not.

My Reflections

In Madre de Dios, I was able to observe the astounding interconnectedness between the environment and human life. Work, food, living situations, education and culture revolve closely around the ecosystem here. Many people provide for their families by using the land’s resources to work as fishermen, boat drivers, loggers and yes, miners. Families also obtain nutritious foods through farming, gardening and hunting, during the current nutritional transition where unhealthier processed foods are being introduced to the area. It has been so interesting to directly observe how the components of the WHO’s One Health triad – animal, human and environmental health – are related here. 

A free-range backyard chicken in one of the villages.
A free-range backyard chicken in one of the villages

I’ve also seen how a family’s physical environment and its remoteness from an urban area determine access to healthcare, education, technology, new opportunities and information. Only about half of the literature on Madre de Dios is written in Spanish, and many articles are located in expensive online databases. Many individuals, who so kindly gave me their chicken feathers, eggs and meat, were both surprised by and interested in my research. Some even shared their takeaways of past Duke research projects in the area. This demonstrated both the community’s desire for more information and their need to see the results of my research. So, to maximize the impact of my research, I plan to post my key findings in Spanish and English on our team’s public website and send them in a fact sheet to health posts and residents in Madre de Dios.

Additionally, I was surprised by my data collection process. Going in, I expected to stroll around markets and quickly get my samples. However, the process of sampling quickly became a complicated and interpersonal endeavor as I discovered the details of, and motives for, rearing poultry. I was also explained the nuances of pollo vs. gallina – both translate to “chicken” in English, but hold distinct meanings. I learned that in this part of the Amazon, as with many other middle-income countries, livestock is more like physical wealth than an abundant food source. Backyard chicken (gallina) can be much more valuable for a household than an equivalent frozen/imported chicken (pollo) purchased from a market. A family’s chickens continually produce eggs (more food to serve at breakfast, or future chickens) and can be consumed or sold when money is tight. These chickens provide sustenance and financial security and are an essential part of life here. To find these free-range local gallinas and buy meat for my analyses, I had to travel to households and family farms. One chicken purchase even led me to a mining camp. Through that and other aspects of my trip, I was able to meet and better understand miners as individuals providing for themselves and their families despite the media’s villainized portrayal of them as a manifestation of environmental destruction and delinquency.

Learning how to butcher a chicken at a mining camp. Credit: Fernanda Machicao ‘22.
Learning how to butcher a chicken at a mining camp (Photo:  Fernanda Machicao)

The interdisciplinary nature of my project has provided me with many valuable experiences. My sampling scheme gave me the opportunity to interact with people I would never have met otherwise. Going door-to-door briefly brought me into the home lives of residents, and the conversations we had taught me so much about their lives, from the food they eat to their family dynamics. As a part of my scientific research, I learned common dishes that incorporate unique chicken parts, different dietary preferences of adults and children and where exactly the food we’ve been eating comes from. I even learned how to raise and butcher chickens. Through this, I was able to understand many important perspectives surrounding culture and food in Madre de Dios.

I am so grateful for everyone who I was able to meet and for the things I learned during my summer fieldwork. I would like to thank Bass Connections, the Center for Latin American and Caribbean Studies (CLACS) and the Duke University Center for International and Global Studies (DUCIGS) for making this experience possible for me.