Legacy and emerging flame retardants in sediments and wastewater treatment plant-derived biosolids

There has been many discussions regarding the utility and efficacy of fire safety standards for consumer products and the use of additive flame retardants (FRs) as solutions to comply with the rigorous standards of at risk materials.

The study by M. Sharkey et al, focuses on the following flame retardant materials, their key chemical components and presence in the Irish countryside.

• Halogenated flame retardants (HFRs) are commonly used in household furniture, electronics, childcare items and insulation foams.
• Brominated flame retardants (BFRs) are largely used in hard plastics from electronic goods, as well as household insulation foams.
• Polychlorinated biphenyls (PCBs) are sparsely used as FRs, but are used in dielectric insulating fluids for capacitors and transformers.
• Chlorinated organophosphate esters (Cl-OPEs) are more commonly found in foams from soft furnishings and childcare products.
• Non-halogenated organophosphate esters (OPEs) have likewise been extensively used in these consumer goods as FRs, as well as a variety of other applications

A culmination of research has concluded that some HFRs, including polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs), meet the criteria for classification as Persistent Organic Pollutants (POPs). Consequently they are deemed to be high risk in terms of environmental persistence and human and ecological toxicity. Their persistent nature in the ecosystem has labelled them colloquially as “forever chemicals”.

Over the last couple of decades we have witnessed the strict regulation of materials and even more stringent fire safety standards, however a few issues still persist. The simplest and cheapest method to adhere to safety standards is usually by the addition of FRs. Substances that have been unequivocally proven to be hazardous to health and the environment have received widespread bans. Unfortunately, it is only recently, many years later that we are beginning to understand the threats posed by alternative FR substances.  These replacements are now seen as “regrettable substitutions”, chemicals with similar properties to their banned predecessors many of whom are now under review by regulatory bodies such as the European Chemicals Agency and the US National Toxicology Programme.

Due to the long lifespan of many of these goods, large volumes of materials containing legacy restricted or emerging HFRs remain in circulation. Eventually these goods enter the waste stream. Meanwhile, goods which no longer use these restricted HFRs have shifted to the aforementioned “regrettable substitutions” for which there is often insufficient ecotoxicological data. Sources of uptake to the environment would likely be from waste handling (e.g. landfills), Waste Water Treatment Plant (WWTP) discharges, domestic water discharges, and industrial emissions from processes where such chemicals are added. The chemicals ultimately end up entering our waste systems most of which are not designed to screen or remove them. Due to their persistence and propensity for long-range transportation, their uptake into the environment is therefore highly likely.

Another potential contamination pathway is through the use of fertilisers produced from the solid fraction of wastewater treatment operations, also known as “biosolids”. Given the high lipophilicity of many BFRs and partial lipophilicity of Cl-OPEs, it is conceivable that these biosolids contain HFRs which are then spread on agricultural lands as fertiliser.