A council has ignored specific questions over why composting bins have been stockpiled but never issued to residents – despite falling recycling figures.
Derry City Council has twice refused to reveal the cost of the bins, how many were purchased and when, and why they have not been distributed to ratepayers.
Hundreds of the brown bins can be seen stacked in rows at the council's public waste and recycling facility at Strathfoyle amid suggestions they were stored there for around 12 months.
The revelation comes as figures show Derry City Council's recycling rates of just under 30% are the second lowest among Northern Ireland's 26 councils.
For the year 2011/12 Belfast achieved just 26.9% recycling, while at the other end of the spectrum, Magherafelt District Council has a recycling rate of 59% – twice that of Derry's.
The amount of household waste sent to landfill in Derry has remained static for years up to 2011/12 at around 70% – above the average of around 58%.
While the council claimed that these rates had improved since last year, campaigners have now called for explanations over what happens to the waste products.
They also want to know why the brown bins were not distributed.
Members of the Zero Waste North West campaign claimed yesterday that some of Derry's waste may be ending up being taken abroad and reused as industrial fuel matter.
Paul Hughes from Enagh Youth Forum said: "I was always under the impression that everything we put into the recycling bins was actually being recycled for use.
"I, like a lot of people, would have made sure to wash everything out before putting it into the bin.
"I think we need to be looking seriously at recycling and how it is done in this area.
"There is obviously some kind of recycling going on, but there needs to be more clarity. There needs to be transparency.
"We also want answers as to why they are not rolling out the brown bins here."
Mr Hughes said that instead of opting for a "quick fix" gassification plant, household black bin waste could be reduced by up to 70% with the brown bins. He was referring to plans for an incinerator which were approved in September 2011, but which only came to wider public attention over recent weeks.
Around 2,000 people have now signed petitions against the plant at Strathfoyle.
Fellow Zero Waste North West campaigner Jim Keys said the group was expecting to hear back from the DoE after flagging up concerns about the application.
A judicial review will be sought if it is not overturned.
A council spokeswoman said: "Council are at present bringing forward plans with regard to food waste collections with the intention of rolling out a scheme to householders in due course.
"Further details of this scheme will be provided once arrangements have been finalised."
She added that all waste activities are undertaken "in full compliance with regulatory obligations" and that all waste collected for recycling "are sent to appropriately consented recycling facilities".
"The council monitors and reviews all of its contracts on a regular basis and is satisfied that none of the recycled materials collected during waste collection activities are taken directly to landfill.
"In addition, waste activities are monitored independently by the Northern Ireland Environment Agency who validate data provided by councils through facility audits, inspections etc.
"Waste arisings locally have reduced substantially over recent years with significant reductions noted in items such as white goods, furniture etc accounting for the majority of the reduction in the overall recycling rates.
"Council is committed to achieving and exceeding landfill and recycling targets and has implemented a range of measures aimed at ensuring this objective.
"In addition, the North West Region Waste Management Group – of which council is a member – are progressing plans to ensure that the group and constituent councils comply with and exceed mandatory EU waste targets."
Significant EU fines could be incurred unless more is done by councils to boost the proportion of material which is reused.
Environment Minister Alex Attwood (below) wants to increase recycling of household, construction and industrial waste to 60% and upwards by 2020.
The European Landfill Directive has set very stringent targets to reduce the amount of waste sent to landfill.
Penalties set by the EU could run into millions of pounds if recycling levels are not met by deadlines.