Whereas a lot of studies have been published on the accumulation of plastics in the aquatic food chain, studies on plastics in the terrestrial ecosystem are scarce. A group of international researchers, led by Esperanza Huerta Lwanga of Wageningen University, published the worldwide first study on field evidence for transfer of plastic debris along a terrestrial food chain.
The study was carried out in Mayan home gardens in Southeast Mexico. Due to an insufficient waste collection system in suburban regions, people burn their plastic waste and incorporate it into the soils of their home gardens. Studying plastic in this terrestrial ecosystem, the authors described that microplastic content increased from soil to earthworm cast to chicken faeces. Furthermore, in chicken crop and gizzard macro- and microplastics were detected with more than 30 particles per gizzard.
Chickens are very important in the diet of the Yucatecan people, which carries a potential risk to human health when local people consume polluted gizzards that are not thoroughly cleaned. Even though washing them does not necessarily remove all plastic debris and chemical residues would not be taken out either. In Mexico, chicken consumption per capita is about 15 chickens per person per year. This translates into an annual ingestion of 840 plastic particles per person. Consumption of domestic chickens (gizzards) around the world in traditional dishes may potentially expose humans to high concentrations of microplastics, either directly by consuming gizzards such as in this study, or through bio-augmented microplastics from the chickens' digestive system into their tissues.