Fate of Plastics in Cattle Digestive Systems

Two herds of cattle at a university teaching farm had plastic fibers in their fecal matter. The source was confirmed to be mineral supplements. When consumed, supplements caused some degradation or fragmentation of plastics.

Plastic products are a ubiquitous part of contemporary consumer products and can contain chemicals like plasticizers, colorings, flame retardants, and antimicrobials. When eaten, these substances can leech from plastics during digestion, and consequently, impact the health of the organisms that consume them. Here, we document plastic contaminants in the form of microfibers (0.5 to 15 mm), that we detected in the fecal matter of two herds of cattle on a college campus. Plastic incidence was similar (41%) for both herds, with a mean of 1 polyethylene microfiber occurring in every 2 g of feces. We confirmed the source of these plastic fibers was the mineral supplements that the cattle have access to year-round and detected the particles in two independent sources of mineral supplements. Despite minor visual changes in the plastic fibers (dulling of the surface) after being exposed to the digestive system of the cows, we were able to chemically confirm (using infrared spectroscopy) that the plastic found in the feces and mineral supplements were identical. To quantify degradation of consumed plastic particles, we performed a digestion study of plastics of similar composition (nylon used to tie square hay bales and polyethylene used to wrap round/rolled bales - not microplastics) used in the farm operations of the university. Following a 54-day exposure to the digestive system of a cannulated bull, we found that the weight of plastics did not change, but significant fragmentation (fraying) occurred. While the physiological consequences of microplastic degradation and potential inclusion among gut tissues are largely unknown, increased surface areas of microplastics from fraying and the leeching of toxic compounds accumulated over long periods of time should be considered as they could influence the safety of beef and dairy products intended for human consumption.