Harbour sludge to be dug up for new tunnel contains alarming levels of toxins Weâre sorry, this service is currently unavailable. Please try again later. Dismiss Save Normal text size Advertisement Sludge on the floor of Sydney Harbour to be dug up during construction of a new harbour tunnel contains alarming levels of toxins, including a âgender bendingâ chemical that caused female sea snails to grow male sex organs. A confidential report shows some of the sludge contains cancer-causing pollutants up to 20 times the safe level for aquatic life, and a banned chemical at 572 times the safe level. High levels of toxins have been discovered in Berrys Bay, where tunnel dredging will occur.