Litter louts are flouting the system of paying fines.
Less than a third of all litter fines issued in the city centre are being paid.
Figures for 2015 show that just 31% of fines were cleared while in 2013, just 1 in 5 was paid.
In one particular area 691 fines were issued but almost 70 tonnes of illegal dumping were collected in the inner city over the Christmas period.
One shop was issued with 70 fines from January 2013 to December 2014.
The annual cost of collecting illegally dumped rubbish is around €650,000.