To apply or not to apply biosolids to land – what are the potential impacts from organic contaminants?
Municipal biosolids are rich in nutrients and can be applied to land to fertilise plants and improve the quality of soil. Approximately 320 000 wet tonnes of biosolids are currently produced by municipal wastewater treatment plants across New Zealand. Of this, an estimated 40% is applied to land, with the remainder disposed of as land-fill or held in long-term on-site storage. Concern about the potential negative effect of biosolid application arising from the presence of pharmaceuticals and other organic contaminants in the biosolids is a barrier to facilitating further beneficial reuse. However, there is also limited knowledge about these contaminants, including their potential environmental effect, in New Zealand.
As part of the Biowaste Research Programme led by ESR with collaborators from Landcare Research, Cawthron Institute, Scion, and Plant and Food, we are investigating the biological impacts of biosolids and biosolid contaminants in the environment using cell-based or in vitro tests, and whole organism tests.
The different types of environmental impacts we are assessing using our in vitro tests include:
- Stimulation of male (androgenic) or female (estrogenic) hormone activity
- Inhibition of male or female hormone activity by anti-androgen or anti-estrogens
- Stimulation of a detoxification enzyme (CYP1A1)
- Mutagenic activity
Our whole organism tests focus on soil organisms, in particular the earthworm, Eisenia fetida (Figure 1) and the springtail, Folsimia candida, since land application is a key beneficial use of biosolids. We assess the reproductive endpoints including cocoon and juvenile production in these test species to assess the long-term (chronic) effect of contaminants.
Our in vitro tests are used to examine the biological activity or toxicity associated with the chemical mixtures found in biosolids collected from municipal wastewater treatment plants across New Zealand. The relative biological activity of organic extracts as measured by the different in vitro tests is shown in Figure 2.
Both our in vitro tests and earthworms tests have been used to assess the toxicity of selected contaminants of concern found in biosolids. These are triclosan, an anti-microbial compound found in soaps, toothpaste, deodorants, and other personal care products, the plasticiser, bisphenol-A, and the pharmaceutical, carbamazepine, used for the treatment of epilepsy and bipolar disorder.
Testing on earthworms showed that bisphenol A had the greatest effect and carbamazepine the least effect on earthworm cocoon and juvenile production. Triclosan caused a decrease in hatching success and number of juveniles per cocoon, while bisphenol-A and carbamazepine had no effect.
Understanding the environmental effects of biosolids and associated contaminants, particularly “new” organic contaminants, will enable the risks and benefits of land application of biosolids to be better assessed. This will inform guidelines for beneficial reuse, including recommended application rates and timing for biosolid application to land.
Jo Cavanagh & Lynn Booth - Landcare Research
Louis Tremblay - Cawthron Institute
Grant Northcott - Plant & Food