Concern over build up of potentially hazardous metals on land
Two separate research studies are examining the environmental impact of spreading sewage sludge on farmland.
The Environmental Protection Agency (EPA) recently published the results of research which provides data and evidence on the sources and scale of microplastic pollution in Irish freshwaters.
Urban wastewater treatment plants were identified as one of the largest point sources of microplastics which are plastic particles less than 5mm in diameter. They are formed either through the breakdown of large plastic particles or through intentional production for products such as cosmetics and cleaning agents.
The research was led Anne Maire McMahon in the Marine and Freshwater Research Centre at Galway Mayo Institute of Technology (GMIT).
She said that landspreading of these sludges on agricultural land poses risks to terrestrial ecosystems and potentially further risks to freshwater systems.
At present, land spreading of sewage sludge is recommended 20 m from lakes and river channels and 10 m from small water courses and domestic wells.
According to the authors of the research, further investigation is required to determine pathways of microplastics entrained in sewage sludge.
When this knowledge has been gained, they recommend an assessment of the ability of the current rules around the use of Biosolids in agriculture which prevent microplastics from entering freshwater systems should be carried out.
Meanwhile, new Teagasc research has concluded that unlegislated metals, PPCPs and microplastics, found to be present in biosolids originating from a selection of Waste Water Treatment Plants, may be inadvertently applied to land.
It found that amounts of two potentially hazardous metals, antimony and tin, for which no legislation currently exists, were much higher than their baseline concentrations in soils, meaning that potentially large amounts of these elements may be applied to the soil without regulation.
The research raises concerns that with multiple applications over several 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.
However, the Teagasc study also found that in general, land-applied biosolids pose no greater threat to water quality than dairy cattle slurry, and cattle exclusion times from biosolidsamended fields may be overly strict.
The production of sewage sludge has increased over the years, and in 2015 more than 58,000 tonnes were produced in the Republic of Ireland.
The treatment and disposal of sewage sludge presents a major challenge in wastewater treatment, and although there are many disposal and reuse pathways, in Ireland up to 80pc is currently reused on agricultural land.