Neither the Department of the Environment nor the Environmental Protection Agency (EPA) knows for sure what happened to it.
“It’s hard to know,” said EPA programme manager Dr Gerry Byrne.
The EPA believes most uncollected rubbish is disposed of legally by householders who take it to landfill sites.
But Dr Byrne conceded people could be burning or illegally dumping the waste.
“I would have a worry people might burn it locally. There is a danger a proportion of it is dumped (illegally),” he said.
The pay-by-weight waste charge system introduced on January 1 could prove a deterrent to those illegally disposing of their waste.
However, the department said there was no evidence “to suggest it is an issue”.
The statistics are contained in the National Waste Database 2003 interim report, published by the EPA recently. It indicates 287,294 tonnes of household waste went uncollected in 2003, an increase of 15% on the previous year.
The statistics are based on estimates given by local authorities, which are obliged to collect domestic waste in their areas.
However, according to the department, local authorities have three grounds on which they can opt out of collecting rubbish: if the cost of providing the service is unreasonable (a problem particularly in rural areas); if the service is privatised; or if the authority is satisfied a householder can safely dispose of waste themselves.
Nationally, 79% of households are served by a collection service, according to the EPA report. In individual local authority areas, the figures range from 100% in the Dublin region to just 45% in Donegal.
The report acknowledges that the potential exists for “backyard burning of waste or other environmentally unfriendly waste practices at the household level”.
The EPA says it has already asked local authorities to focus on the issue in their waste management plans.
However, a spokesman for the department said there were no indications it was a problem.
“There’s nothing to suggest in that statistic that most of these people aren’t disposing of it in a proper, legal way,” he said.