However, after consulting various bodies about the practice, shortcomings emerged over its tracking and recording.

The Department of Housing said: “Sewage sludge is useful as a fertiliser. EU rules promote the use of sewage sludge in agriculture, but regulate its use to prevent any harmful effects on soil, vegetation, animals and people.

“The EU Sludge Directive is currently being evaluated by the EU Commission, it’s expected a revision will be made.

“In Ireland... the Good Agricultural Practice Regulations require farmers that apply sludge to land to include the nitrogen and phosphorus loadings in their nutrient calculations for compliance with the regulations.

“The management of sludge is a matter for Irish Water,” the spokesperson said.

When asked about the process, farms selected, and volumes used per sector in 2019/2020, Irish Water was unable to provide full details.

A spokesperson said it works with third-party “sludge contractors” to manage the re-use of wastewater sludge in line with the code of practice for the use of biosolids in agriculture.

“Contractors… providing sludge management services for Irish Water have been submitting information regarding individual farms since 2016.

“Over the course of the framework 286 farms have received biosolids. This changes on a yearly basis.

While Irish Water said “there are huge benefits” in applying sludge to land, including “a reduction in chemical fertilisers”, it said Bord Bia quality-assured farms “prohibit” its use.

Irish Water said “the Department of Environment is responsible for managing the nutrient management plans submitted by sludge contractors”.

However, an Environment spokesperson said “this query is a matter for Department of Housing”.

Then, a Housing spokesperson said “this information is maintained by all local authorities”.

“Each local authority is required to maintain a sludge register, which details where sludge was used in a calendar year.

“In a high proportion of cases, sludge goes onto tillage or grassland where it has been ploughed for re-seeding.”

The Department of Agriculture only receives information on sludge when applied to a derogation farm.

When asked if greater oversight is needed, Housing said: “The use of biosolids is not considered a significant risk to water quality, except in cases where the method of application does not comply with regulations.

“The Department has not been notified of any significant issues with the controls on biosolids by Irish Water or the local authorities.”

However, a source claimed “there is no oversight which makes the system open to exploitation”.

“Sewage sludge is a law unto itself. It’s not that authorities are hiding the information — they simply don’t know what’s going on.

“The finger always points at farming, yet here is this other stuff. There may not be a huge volume, but we don’t know where it is, or its impact. It’s a dark hole that nobody is down.”
Advice

Bord Bia acknowledged that treated sludge “can minimise the need for chemical fertiliser”, but its advice remains on “switching to protected urea”.

Highlighting a recent Teagasc study on sludge, Bord Bia said: “Although, in general, land-applied biosolids pose no greater threat to water quality than dairy cattle slurry… a matter of concern is that unlegislated metals, pharmaceuticals and personal care products, and microplastics found to be present in biosolids originating from a selection of plants examined in this study, may be inadvertently applied to land.

“With multiple applications over years, these may build up in the soil and enter the food chain, raising concerns over the continued application of biosolids to land in Ireland.”