Answer: The biologist is working on ecosystem level of ecological study.
Step-by-step explanation:
The ecosystem of ecological study Is the study that comprises of the large communities of living organisms i.e plants, animals, microbes also called the biotic factors interacting or linked with the non living aspects of the environment known as abiotic factors. The known living aspects are water, soil, air e.t.c.
The biologists study is an ecosystem level of ecological system because He or she is studying toxin flow from biotic factors to abiotic factors.