At which trophic level would the highest accumulation of a non-biodegradable substance occur?

The highest accumulation of a non-biodegradable substance would occur in the trophic level of tertiary consumers. This is because non-biodegradable substances, such as heavy metals or persistent organic pollutants, tend to accumulate in the bodies of organisms over time, and as we move up the food chain, the concentration of these substances becomes increasingly magnified. Tertiary consumers are at the top of the food chain, and thus, they accumulate the highest concentrations of non-biodegradable substances.