Sediment of a pond was suspected to contain the contaminant Z. Sediment chemistry analysis detected presence of 2 but at a level just above the lower threshold but befow the upper threshold of the sediment guidance value for Z (class B ). There have been a series of reports of decrease in benthic organism diversity with a few species known to be sensitive to Z disappearing in the past few years. Do you think the contaminant Z in the pond is responsible for the decline in benthic organism? is there any other test you can do to support or disapprove your conclusion?.