Environment and Ecosystem — quick quiz

In a pond ecosystem, the biomass (total dry weight of organisms) at different trophic levels was measured. The measurements were: Phytoplankton (producers) = 1000 kg, Zooplankton (primary consumers) = 100 kg, Small fish (secondary consumers) = 10 kg, Large fish (tertiary consumers) = 1 kg. If pesticides are introduced into the pond and accumulate in organisms without being broken down, in which organisms will the concentration of pesticides be highest?