Keeping track of a chemical world

We are ever more reliant on chemicals in both the products we use and the medicines we take, but do we know what happens when they end up in the water supply? Greg Pilbrow takes up the case…

The environment often bears the brunt of human activities. Whilst we treat domestic wastewater to remove the major pollutants – BOD, ammonia, phosphorus and nitrate – there are many trace contaminants from our pharmaceutical and personal care products whose ultimate fate in treatment processes and final disposal routes we still do not fully understand.

However, new initiatives in interdisciplinary research are helping progress in this field of environmental science. We use microorganisms to treat industrial and domestic wastewaters. Methanobacterium spp and Methanococcus spp generate biogas in anaerobic digestors, Rhodococcus is capable of breaking down oil spills¹ whilst activated sludge, the most widely used process for biological treatment of wastewater uses a wide range of aerobic bacteria, amoeba and protozoans to oxidise carbonaceous material to carbon dioxide and water. All of these processes produce a sludge comprised of surplus biomass (bacterial cells) together with adsorbed organic molecules. A collaborative research project between AstraZeneca’s Brixham Environmental Laboratory and the University of Portsmouth has examined sewage treatment sludges to try to understand how active pharmaceutical ingredients (APIs) in our domestic wastewater, partition between wastewater sludges and liquors². This is critical to keeping track of how these potentially toxic species might escape detection and their eventual fate in the environment.

Methanobacterium spp and Methanococcus spp generate biogas in anaerobic digestors, Rhodococcus is capable of breaking down oil spills

Existing models for predicting where and how APIs disappear often fall short, which is why this recent research collaboration has been so important. Whilst analytical techniques for detecting trace contaminants in the aqueous phase are typically very robust, detection in sludge is more difficult. APIs and other potentially harmful contaminants can be missed by wastewater detection systems if they are adsorbed onto sludge components. They can then be released at a later date to wreak all manner of environmental problems. Some of the models employed for predicting the impact of this process can lack accuracy, occasionally failing to predict real-world effects and consequences, especially when it comes to the indirect metabolites and derivatives of pharmaceutical products in wastewater. What is so important about the work of the AstraZeneca and University of Portsmouth team is that they have developed a solid-phase extraction (SPE) method that can rapidly determine API-sludge interactions from just a half-gram sample³. Existing models of API-sludge interactions tend to place an emphasis on hydrophobic interactions. While these are an important consideration when dealing with neutral organic compounds, when it comes to ionisable compounds (like many APIs) this model fails to give reliable predictions. Using the SPE method, the researchers demonstrated that additional interactions, such as ion-exchange, pi-pi and H-bonding, are just as important as hydrophobic interactions when examining API adsorption mechanisms during wastewater treatment. Including findings like these into existing and future models of API-sludge interactions will help to generate behaviour predictions that are much more accurate.

Pharmaceutical products tend to attract a great deal of notoriety in the media when it comes to pollution, but other trace contaminants can be just as significant. Whilst the current generation of wastewater treatment processes achieve good control of the major pollutants, they are less effective when it comes to the more subtle contaminants like heavy metals such as silver, cobalt or nickel. Although many of these metals can be toxic, some are required in small amounts by most organisms to survive. This dichotomy makes accurately monitoring them a difficult task, and in developing countries still either implementing or optimising their wastewater treatment plants, the contamination of surface waters with these potentially toxic metals is a concern. To make matters worse, detection of multiple metals – often in the parts per billion (ppb) range – can be challenging and time consuming.

[caption id="attachment_53503" align="alignnone" width="620"] Advances in detection data will enable scientists to more accurately locate traces metals.[/caption]

Combating this challenge is a team from the University of Sindh. Theirs is the first study to provide evidence on the influence of industrial effluent on silver and heavy metal concentrations in the surrounding freshwaters of Pakistan?. The team used single-step cloud point extraction coupled with flame atomic absorption spectrometry (FAAS), along with micelles made of Triton-X to successfully entrap and isolate the metal chelates that had reacted with ammonium pyrrolidinedithiocarbamate (APDC). With this method, the researchers were able to detect silver, cadmium, nickel, cobalt and lead simultaneously, right down to levels of 0.42, 0.48, 0.92, 0.62, and 1.42 ?g/L, respectively. Their research also highlighted how metal concentrations varied spatially and were subject to dilution from other abiotic factors like canal run-off and sediment erosion. These detection data will enable future studies to rapidly identify and monitor heavy metal pollutants, which will help in facilitating the formulation of effective management strategies.

Whilst the current generation of wastewater treatment processes achieve good control of the major pollutants, they are less effective when it comes to the more subtle contaminants like heavy metals such as silver, cobalt or nickel.

We are now more aware than ever of our own impacts on the planet and the conservation efforts required to help manage and remedy these. To support this huge surge in interest, industry and academia alike have responded with the development of a wealth of innovative techniques and equipment to better monitor, understand and ultimately protect our environment. The crucial ingredient in all of this research is ultrapure water. Analysis at microgramme per litre concentrations requires sample blanks and reagents at least an order of magnitude purer – Type 1+ laboratory water.

Author: Greg Pilbrow is sales director at Veolia Water Technologies Contact: www.veoliawatertechnologies.co.uk

References

1 Pen, Y. et al., 2015. Effect of extracellular polymeric substances on the mechanical properties of Rhodococcus. Biochimica et Biophysica Acta (BBA) - Biomembranes, 1848(2), pp.518–526.

2 Berthod, L. et al 2016. Effect of sewage sludge type on the partitioning behaviour of pharmaceuticals: a meta-analysis Environ. Sci.: Water Res. Technol. 2016, (2), pp.154-163

3 Berthod, L., Roberts, G. & Mills, G. a., 2014. A solid-phase extraction approach for the identification of pharmaceutical–sludge adsorption mechanisms. Journal of Pharmaceutical Analysis, 4(2), pp.117–124.

4 Naeemullah, K. et al., 2014. Simultaneous determination of silver and other heavy metals in aquatic environment receiving wastewater from industrial area, applying an enrichment method. Arabian Journal of Chemistry.