Biosolids

ASSESSMENT OF EMERGENT CONTAMINANTS IN BIOSOLIDS  
Recommended PFOS and PFOA levels in biosolids for land application
P Darvodelsky, K Hopewell
Publication Date (Web): 5 September2018
DOI: https://doi.org/10.21139/wej.2018.027


The water industry monitors potential risks from new compounds to ensure biosolids can be used sustainably. PFOS and PFOA (perfluorooctane sulphonate and perfluorooctanoic acid) have known or suspected health effects and have been detected at levels of concern in a number of communities around Australia. These compounds are two of the most well-known of the group known as per-and polyfluorinated alkyl substances (PFAS).

The Australian and New Zealand Biosolids Partnership (ANZBP) conducted a national survey of available data on the presence of PFAS in biosolids in which major utilities shared their data from over 100 samples from 13 different sewage treatment plants around Australia.
In Australia, the National Environment Protection (Assessment of Contaminated Sites) Measure (NEPC, 1999), or NEPM sets out a clear method for assessing emerging contaminants. This method is used as the basis for determining ‘safe’ levels of PFOS and PFOA in biosolids.

This review examines two key exposure pathways:

• Direct ingestion of biosolids;
• Direct ingestion of soil in which biosolids have been incorporated.

It is considered in the context of Australian biosolids guidelines and use that these two exposure pathways are likely the highest risk pathways, however, it should be noted that insufficient information on factors such as crop and animal uptake rates currently exist to accurately assess other exposure pathways. These pathways are important and should also be reviewed as data becomes available.

The key steps to determine safe limits in biosolids are to:

  1. Use the tolerable daily intake levels of PFOS and PFOA set by Australian Department of Health;
  2. Use the NEPM method to calculate the health investigation level (HIL) for PFOS/PFOA (direct ingestion);
  3. Assume typical biosolids application rate, repeat application frequency and incorporation depth for biosolids applied to land;
  4. Calculate allowable safe levels of PFOS/PFOA in biosolids applied to agricultural land.

Results from the survey are summarised in Table 1 below.

Table 1
Table 1: Recommended Values for PFOS and PFOA in biosolids for use on agricultural land

The conclusions of this review and analysis are:

  1. PFOS and PFOA occur in biosolids at detectable levels. PFOS and PFOA were detected in 92 out of 109 samples from 13 different Australian sewage treatment plants;
  2. PFOS was detected above the NEPM HIL at two sites (3 out of 109 samples) with known PFOS contamination issues. Average values of PFOS measured in Australian biosolids were around 7% of the calculated Health Investigation Level;
  3. The data shows that PFOS can occur at sites with contamination issues and this highlights the need for further investigation and monitoring of PFOS in Australian biosolids;
  4. The levels of PFOA detected in this review are significantly lower than HILs calculated. This data suggests that there is little need to monitor PFOA in biosolids with the maximum recorded value of PFOA being around 2% of calculated HIL;

Recommendations

It is recommended that limits for PFOS in biosolids be adopted as set out in the table below and reviewed regularly on the basis of further data on the levels of PFOS in biosolids.

Table 2
Table 2: Recommended PFOS limits in biosolids for different end uses

Notes: 
1) mg per kg of dry weight of biosolids
2) NSW, QLD, ACT, SA guideline terminology (also TAS for Grade A)
3) National, VIC, WA guideline terminology
4) TAS guideline terminology


It is recommended that PFOS is routinely measured in biosolids.
It is recommended that PFOA is not routinely measured in biosolids.
It is recommended that other exposure pathways for PFOS, PFOA and other PFAS be investigated as and when the necessary information becomes available.
It is recommended that sites with a known history of PFOS and/or PFOA contamination should monitor these compounds on a case by case basis.
 

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