Monday, 15 June 2020

Environment Agency report finds biosolids contaminated with multiple pollutants

UK Environment Agency report finds sewage sludge destined for farms contaminated with multiple pollutants

Below are some of the highlights from the new report -

On the composition of Sewage Sludge / Biosolids - 

“There is growing skepticism whether land application of sewage sludge is a sustainable method of dealing with that waste stream. The underlying concerns for these actions result in particular from the fact that the majority of contaminants in general and organic contaminants in particular potentially contained in sewage sludge are not known and not sufficiently tested before applying sludge on land. An extensive and meaningful risk assessment would require however full knowledge of the number, the concentration and the effects of all organic contaminants found in sewage sludge. Filling the gaps in knowledge regarding the concentration, fate and toxicity of sludge-borne contaminants is critical if risks associated with land application are to be adequately characterized”.
"in addition to organic waste material there are traces of other substances, some of which can be toxic to humans and animals at elevated concentrations in the soil or in food. The composition of sludge is thought to be becoming increasingly complex"

"Smith (2009) identified the following compounds, which may be incorporated in sewage sludge:
·persistent compounds from incomplete combustion of fossil fuels that enter the urban wastewater collection system through deposition onto paved surfaces via run-off (e.g. polycyclic aromatic hydrocarbons (PAHs) and dioxins / furans);
·persistent compounds that are associated with impurities in wood preservatives such as creosote (PAHs) and pentachlorophenol (PCP) that enter urban wastewater in run-off;
·controlled persistent compounds mobilized by volatilisation from soil, deposition and transfer to urban wastewater in run-off (e.g. PAHs, PCBs and dioxins / furans);
persistent compounds generated by cooking food that are discharged from domestic sources
(e.g. PAHs);
·persistent compounds that are prohibited from use/manufacture, but domestic sources may exist and can transfer to urban wastewater via run-off (e.g. chlorinated pesticides);
·compounds discharged to sewer used directly in industrial processes or domestically, including solvents, flame retardants or compounds that leach from plastics and surfaces during end-use and are carried in run-off (e.g. di(2-ethylhexyl)phthalate (DEHP) and polybrominated diphenyl ethers (PBDEs));
detergent residues (e.g. linear alkylbenzene sulphonates, nonylphenol and nonylphenol
·pharmaceuticals, antibiotics, endogenous hormones and synthetic steroids; and,

·compounds from the various above groups with endocrine-disrupting potential.

Microplastics are also a growing concern. These can be split into two groups (CIWEM, 2017):
·primary microplastics include industrial scrubbers used in blast cleaning, plastic powders used in moulding, nanoparticles used in industrial processes and micro-beads used in cosmetics and personal care products. Soaps are a major source of microbeads both in personal care products (e.g. deodorant, shampoo, conditioner, shower gel, lipstick, hair colouring, shaving cream, sunscreen, insect repellent, anti-wrinkle creams, moisturizers, hair spray, facial masks, baby care products, eye shadow, mascara) and in detergents for washing machines;  

-and secondary microplastics formed by fragmentation and weathering of larger plastic items during the use of products such as textiles (including microfleece materials), paint and tyres, or once these or other plastic items (bags, bottles etc.) have been released into the environment.

Most microplastic emissions occur in urban and residential areas. In developed regions,
municipal/industrial effluents and even diffuse urban runoff are eventually conveyed to wastewater treatment works. Additives used in manufacture include, PCBs, polybrominated diphenyl ethers (PBDEs), perfluorooctanoic acid (PFOA), bis-phenol A (BPA) and phthalate plasticisers. Microplastics could also provide a medium for exotic species and pathogens, for example microorganisms developing biofilms on microplastics particles. (UNEP, 2015).
During wastewater treatment, over 90% of microplastics are retained in sewage sludge (Carr, 2016). Most of the plastic ingredients in microplastics contain non-degradable polymers, which may take hundreds of years to degrade completely via oxidative or photodegradation routes (UNEP, 2015). In most urban and domestic environments, the contact time for these chemicals with human users will be in the order of minutes to days, with most of the chemical residues following usage being washed into sewers. However, once partitioned into sludge and spread to land, the residence time for some of the more persistent chemicals in agricultural soils can be many years. Sludge also contains bacteria and viruses, which are a potential hazard to the health of humans, animals and plants"

"The assessment indicated potential risks to human health from the following POP: benzo(a)pyrene, dioxins, furans and dioxin-like PCBs, plus PTE manganese.
There were also potential issues with enrichment of a wider range of PTE and POP, which may indicate that long term spreading of sludges at the modelled rates could result in accumulation of these contaminants to levels which may pose a risk"

Potential Risks

Risks to human health or environmental receptors as a result of waste material applied to land can be categorized as:
·contamination of soil by substances harmful to human health, crops or livestock;
·contamination of groundwater by substances harmful to human health or ecological receptors;
·contamination of surface water by substances harmful to human health or ecological receptors;
·contamination of the food chain by substances harmful to human or animal health; or

·reduction in the agricultural productivity of land.

A further limitation is that for many of the emerging toxics, not enough is understood about the toxicity and behaviour of these contaminants in the environment to derive suitable risk assessment criteria which are protective of human health, crops, livestock, controlled waters, and the wider environment.

The contaminants present in materials applied to land can be broadly categorised as:
·potentially toxic elements (PTEs), predominantly metals, which have long been recognised as hazards and which are typically included in the thresholds for compost and sludge;
·other inorganic compounds (e.g. various anions and nutrients) which may affect soil quality or agricultural productivity, or which may affect biological processes.
organic contaminants, many of which are persistent in the environment and some of which may bioaccumulate. Some of these chemicals are widely recognised as hazards (e.g. dioxins and PAHs) and are often analysed for in wastes, although are not included in the thresholds for compost, digestate and sludge. Others, such as PFAS and pharmaceutical residues, are not routinely analysed and do not have well-established thresholds;
·physical contaminants such as glass and plastics, which may pose health and safety risks, and in the case of plastics and microplastics release chemicals of concern upon degradation and breakdown; and
·asbestos, the health risks for which are well known.

Organic Contaminants

“organic compounds are present in many of the materials that are ultimately applied to land, and in many cases these are of anthropogenic origin.
The diversity of materials and their sources of origin makes it difficult to make definitive assessments at this stage of how these compounds find their way into certain materials. Some (such as PAHs and PCBs) seem to be ubiquitous, albeit at usually low concentrations. The absence of regulatory thresholds for many compounds means that it is difficult to determine whether non-detects (at current detection levels) are actually indicative of negligible risk.

It is also worth noting that the relative half-life of the compounds when assessing risk is important. For example, volatile aromatic compounds (e.g. toluene) may be present in waste at low levels but are anticipated to break down relatively quickly in soil, whereas other compounds such as PCBs, PBDEs, PFOS, dioxins and furans have very long half-lives in soil and can last for years. With these persistent chemicals of concern, there is the possibility for accumulation in soil and bioaccumulation in animals and humans ingesting grass and crops grown on the soil. Based on the M2L and WEP studies, the most widespread organic contaminants in wastes includes:
·dioxins and furans;
·triclosan; and


“The potential presence of microplastics in wastewater is becoming a concern, as these can then become incorporated into biosolids and sewage sludge which is then spread to land.
Microplastics can potentially impact soil ecosystems, crops and livestock either directly or through the toxic and endocrine-disrupting substances added during plastics manufacturing.
During use, plasticpolymers efficiently accumulate other harmful pollutants from the surrounding environment, including a number of persistent, bioaccumulative and toxic substances, e.g. PCBs, dioxins, DDTs and PAHs (Nizetto, 2016). As yet, there is no standardised method for assessing the levels of microplastics in wastewaters, sludges and soils and consequently the presence of microplastics in wastes and agricultural soils was not assessed and the full potential extent of the issue has not been properly assessed.
...the possible presence of plastics can be inferred from the detection of

certain organic contaminants present in plastics (e.g. phthalates, used as plasticisers), but the presence of micro-plastics and whether or not these are acting as “sponges” for adsorption of other organic contaminants is not clear.

"the cumulative effect of enrichment from multiple applications of waste over a number of
years has yet to be assessed, Currently, the guidance in the regulations requires analysis of
PTE (potentially toxic elements ) concentrations in receiving soils once every twentieth year.
The levels of enrichment identified for individual spreading events are sufficiently high that
year on year applications could result in significant increases in PTE concentrations in the 20 year period between testing, to the extent that the soil may no longer be suitable for supporting crop growth.

In addition, the PTE suite does not include all of the potential contaminants present in waste which may pose a risk to human health, controlled waters, and the wider environment.

Ecological risks were assessed by screening soil concentrations against Soil Screening Values (SSV) derived for assessing potential risks to ecological systems from 11 contaminants including benzo(a)pyrene, pentachlorophenol, toluene and selected metals (EA, 2008). The SSVs are conservative and are to be used for screening to provide an early indication of the potential for risks to exist. Concentrations of contaminants exceeding the SSVs may indicate a concern, which may warrant further investigation or risk evaluation.
However, the following contaminants were identified at levels that may present a risk to human health:
·dioxins and furans; and

It is becoming clear from the results and other studies that there are other contaminants
present in waste whose effects in soil environments have not been well studied and there remains significant uncertainty regarding the potential longer term impacts of these contaminants on the quality of the land bank, and the potential for bioaccumulation of more persistent organic contaminants within receiving soils, and potentially crops grown on the receiving soils.

...Particular concerns revolve around the role of anti-microbial chemicals and the effect which these could have on naturally occurring soil bacteria and fauna intrinsic in maintaining healthy soil conditions.

...While the presence and behaviour of nutrients (particularly nitrate) and more established
contaminants such as heavy metals in controlled waters are well understood, there is little information regarding the current levels, risks and impacts from emerging toxics and other organic pollutants which could be present in wastes being spread to land and ultimately end up in surface water, groundwater and the marine environment.

... but perhaps the biggest risk to the landbank is from the spreading and incorporation
of physical contaminants into agricultural soils (for example plastics, microplastics)
Coupled with advances in pharmaceutical and healthcare industries, there is an ongoing shift away from the more well understood traditional contaminants (i.e. heavy metals) to an ever increasing list of new chemicals, whose behaviour in the environment is not well understood.

In addition to the emerging toxics (including phthalates, antimicrobials, personal care products) there is also evidence of many persistent organic pollutants

As our understanding of the behaviour and longevity of some contaminants in the natural environment has improved (and continues to do so), the number of potential contaminants present in wastes and soils, which may pose a risk to human health and the wider environment, has expanded. Our knowledge is continually evolving and currently includes the following as a non-exhaustive list: PAHs, PCBs, dioxins and furans, Per- and Polyfluoroalkylated Substances (PFAS e.g. PFOS and PFOA), PDBEs, phthalates,
antibiotics, human and veterinary medicines, pesticides, and antimicrobial chemicals.
In addition to chemical constituents of waste, there are also concerns over physical contaminants particularly with regard to plastics and microplastics. The latter are of particular concern due to their small size, ability to be retained by WwTW (Carr et al., 2016), and ability to potentially sequester other contaminants (e.g. PCBs, dioxins, DDTs and PAHs) which are subsequently released as the plastics break down in soils (Nizetto at al., 2016).

The fate and behaviour of many of these compounds in the soil environment are only beginning to be investigated, and the risks associated with these contaminants is not yet understood. Current testing suites for characterising wastes and soils remain largely unchanged, despite increasing evidence of the identification of low levels of contaminants in waste streams.

There are uncertainties over the levels of these contaminants present in wastes spread to land. Specifically, there is uncertainty over whether these contaminants pose a risk to human health and the wider environment, either at the levels present in wastes or through enrichment in soils due to repeated applications over successive years."

No comments: