A new membrane-based passive sampler allows detecting faecal sources of pollution (Baan)

By Ines Almeida

Ammonia passive sampler being deployed by Cameron Amos.

Figure 1: Ammonia PIM-based passive samplers being deployed by Cameron Amos.

The presence of ammonia in aquatic systems is often the result of the decomposition of organic matter or the release of ammonia rich agricultural, industrial and domestic effluents. Ammonia is harmful to aquatic organisms and its concentration is an important water quality parameter. It is also an indicator of faecal pollution. The most common sampling method used to monitor ammonia or other pollutants in water environments is based on the collection of samples in a particular moment in time, also called ‘spot sampling’. However, pollution events are likely to be missed if they occur between spot sampling. The risk of this happening can be minimized if spot sampling is conducted at higher frequency. However, this will increase substantially the costs of the overall monitoring programme.

Ammonia is an important water quality parameter.

Passive sampling is a sampling method that allows the measurement of the time-weighted average (TWA) concentration of pollutants for an extended period of time (e.g. days, weeks or even months). Episodic pollution events can thus be more easily detected, and monitoring costs can be considerably reduced.

In this context, we have developed a passive sampler for ammonia monitoring in freshwater aquatic systems (e.g. creeks, stormwater drains) using a polymer inclusion membrane (PIM) [1]. The PIM was used as the semi-permeable barrier between the sampled medium (i.e. aquatic system) and an acidic receiving solution, located in the sampler’s glass container (Fig. 2). This PIM contained the extractant dinonylnaphthalene sulfonic acid, responsible for binding with ammonia (as ammonium ion, NH4+), and transporting it across the membrane into the receiving solution.

The PIM is used as a semi-permeable barrier in the sampler and is selective towards ammonia

These samplers have been studied and calibrated under laboratory conditions and applied successfully in a field monitoring programme with the aim of identifying the origin of microbial contamination in Frankston’s and Mornington Peninsula’s stormwater drains (Fig. 1). Episodic faecal pollution events could to be detected by the ammonia PIM-based passive samplers, while in the majority of the cases the same events were missed when doing spot sampling.

Passive sampler

Figure 2: A) PIM-based passive sampling device (the glass container accommodates the receiving solution). B) Floating structure with three passive samplers attached (used in field applications). C) Passive sampler screw cap accommodating the polymer inclusion membrane (PIM).

[1] Almeida MIGS, Silva AML, Coleman RA, Pettigrove VJ, Cattrall RW and Kolev SD (2016). Development of a passive sampler based on a polymer inclusion membrane for total ammonia monitoring in freshwaters. Analytical and Bioanalytical Chemistry 408(12):3213-3222.

For more information contact Ines Almeida: mariads@unimelb.edu.au.