The article discusses how chemicals accumulate in fish and increase in concentration as they move up the food chain. The researchers used models to study how different factors affect this process. They found that for less oily chemicals, looking at concentrations normalized to lipid content is most helpful. For more oily chemicals, looking at wet weight concentrations is better. They also found that the rate of biotransformation plays a crucial role in how chemicals move through a food chain. The researchers suggest using a combination of field studies, lab experiments, and modeling to better understand how chemicals build up in ecosystems.