QuEChERS – an alternative approach to monitoring environmental pollution?

What is pollution?
The Oxford English Dictionary states that this is ‘the introduction of harmful substances or products into the environment’ [1]. This description automatically conjures images of the Exon Valdez oil spill or big fume clouds over a city. However, a pollutant can be something as small and insignificant as a common pharmaceutical, or even the active component within a household cleaning product.  Just take a moment to think about the pharmaceuticals you have in your cupboards at home; paracetamol, ibuprofen, aspirin or maybe hay fever medicines such as loratadine or cetirizine. What about cleaning or personal care products? Have you ever thought about what happens to these products once they’ve been used?
Like any foodstuff, once a drug has been taken it is excreted from the body into the wastewater system with other household waste. While it was initially thought that small molecules, like pharmaceuticals, are degraded during wastewater treatment, research has shown this isn’t the case.  So why is this such a problem? Similarly to domestic recycling that we are all required to undertake, waste is often more manageable when separated.  Wastewater is no different and is segregated as solid and liquid fractions following (or as part of) treatment; water is then released into water courses with the majority (80%) of treated solids (sludge) recycled back onto agricultural land as fertiliser [2] and the remainder often placed in landfill. Given this recycling process, there is a potential for pollutants present within these wastewater fractions to bioaccumulate and enter the food chain through agricultural and fishery stock.  It is therefore key that we do not underestimate the impact of our waste on environmental and public health.  Already there have been global reports of the adverse effects of pharmaceuticals on the animal kingdom. For example, the non-steroidal anti-inflammatory, diclofenac, has caused multiple species of vulture in Asia to become critically endangered [3] with the Indian long-billed vulture and red-headed vulture populations showing a decrease of 97-99% [4]. The female contraceptive pill is another with longstanding environmental impact, feminising male fish causing a rapid decrease in population over a 2 year monitoring period [5]. Due to the demands for environmental monitoring programmes, more candidate pollutants are being discovered in recycled waste with a significant potential impact for both environmental and public health.  For example, biocides have been linked to a number of ailments, from skin irritation to breathing disorders [6,7], and the use of tributyltin (TBT), an antifouling agent, has been shown to have a long-lasting impact on marine eco-systems [8]. This information alone begs the questions ‘if’ and ‘at what point’ our behaviour will have an impact on human health if nothing changes?

Regulation
The introduction of the Water Framework Directive (2000/60/EC)) in 2000 was a ‘game-changer’ for environmental monitoring. Member states were now obligated to look at the environment with a more holistic approach, considering the impact of environmental pollution on the ecosystem as a whole.  This included water courses but also land and organisms living in these catchments such as biota. Information gathered from monitoring programmes following the introduction of this policy led to the development of environmental standards for hazardous substances, the environmental quality standards directive (EQSD) (2008/105/EC). The Chemical Investigation Programme (CIP), established in 2009, was a UK based initiative aimed at developing these directives to identify and understand the prevalence of potential pollutants within wastewater samples to set quality standards in wastewater. The initial CIP study highlighted substances, including a selection of pharmaceuticals, of emerging concern to environmental pollution that are not yet subject to legislation but specified on a “watch list”. These substances include three pharmaceuticals and are subject to a monitoring programme, gathering data to determine the risk within the environment.
In 2015, CIP II was launched to investigate these pharmaceuticals and a broader scope of compounds of potential environmental concern, focusing on their levels in environmental samples to inform policy [9].

The sample preparation problem
To determine the extent of pharmaceutical pollution the content within environmental sample matrices first needs to be established using a suitable sample preparation method. Similarly to the principles of waste recycling, a key objective of sample preparation for trace analysis will be separation – enabling the detection of trace materials (albeit with potentially higher potency) than more abundant materials.  Current recognised methods for preparing complex environmental matrices such as soil and wastewater effluent for analysis are typically multi-step procedures using a range of techniques and apparatus, resulting in methods that are time and resource consuming, unsuitable for high-throughput analysis. Our work has investigated a new approach to preparing samples for monitoring levels of commonly used pharmaceuticals in environmental samples, as detailed by UK Water Industry Research and the Chemical Investigation Programme. These have been included along with other chemicals (biocides) commonly used in a domestic capacity that may contribute to pollution levels in wastewater.  The Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) protocol is a sample preparation method developed by Michelangelo Anastassiades and Steven Lehotay for the extraction of pesticides from fruits and vegetables [10]. Compared to recognised environmental preparative methods for wastewater and solid samples, this approach potentially offers a reduction in: 1) preparation time, from hours to ~20 minutes per sample and, 2) cost, estimated at 63% for the extraction cartridges alone.  It is therefore, prudent to investigate the potential of the QuEChERS method further as an example of a translational approach of sample preparation.   
The method consists of a two-step extraction; 1) a liquid partition into acetonitrile with the addition of drying agents, salts and buffers to limit polar interferences and facilitate phase transfer respectively, followed by, 2) a dispersive solid-phase extraction (dSPE) for further interference removal (see figure 1). There are two buffered methods, that recognised by AOAC (using sodium acetate salt) and the EN method (a combination of sodium chloride salt and sodium citrate buffers). We have modified the QuEChERS protocol for the extraction of a suite of pharmaceuticals and biocides by adopting ingredients of the different methods, i.e., using 4 g of magnesium sulphate and
1.5 g of sodium acetate.  To assess the extraction performance, the matrix effects (%ME) and recovery (%REC) of each compound was investigated in water and soil samples fortified with a mixture of pharmaceuticals and biocides.  These were prepared as three sets of quality control samples (QCs) containing known amounts of analyte using a ‘spike before’ and ‘spike after’ extraction approach for recovery, along with a non-extracted QC to measure matrix effects [11].  For an ideal preparative method we would look to achieve the following: 1) repeatable data (%ME and %REC), 2) low matrix effects (~100%) and, 3) high analyte recoveries.  To understand the potential for reducing costs further and offering better alignment with the needs of clinical samples, we have also undertaken a ‘proof-of-concept’ study using lower sample volumes and extraction materials as ‘miniaturised’ mini-QuEChERS method.

Results
The QuEChERS extraction has shown considerable flexibility for method development and application with efficacy for different chemical substances and sample matrices.  This is evidenced in example (pilot) data (figure 2) illustrating the extraction of common pharmaceuticals and biocides of variable lipophilicity/acidity, using higher sample volumes of 4 mL typical of environmental matrices. The analytes were extracted with reasonable precision (relative standard deviation (RSD) of <20% for most pharmaceuticals and biocides tested) and a median recovery value of 48.9% for the suite.  Importantly, there appears to be reasonable control of matrix effects for these compounds (values ~100%, with precision of <20%RSD) enabling a more meaningful recovery measure to be drawn from the extraction.  Interestingly, when the scale of the extraction is reduced in terms of sample volume and extraction material the data appears to show an optimum operating condition.  For data acquired with a 1 mL sample volume (see figure 2) each metric of performance typically improved for all compounds studied showing precision <20%RSD, minimal matrix effects (median 103.9%), and improved recovery (median 53.2%)).  This is pleasing, providing evidence that this approach has the potential for application in other areas of science where considerably less sample volume is available (e.g. clinical) unlike that conventionally associated with environmental samples. The method has also shown significant promise in extracting certain environmental samples; QuEChERS has shown similar repeatability of performance in soil (relative standard deviation (RSD) of <20% for the majority of pharmaceuticals and biocides) with a median recovery value of 56.4% for the suite (see figure 3). This provides promise of a workable method in monitoring receiving land for chemical contamination following wastewater sludge deposition.          

Conclusion
This sample preparation method has shown efficacy in extracting different chemistries with data presented here concerning a small selection of pharmaceuticals (of environmental interest) and surfactant biocides.  Using higher sample volumes (4 mL) most compounds (7/9) showed good precision (RSD<20%), matrix effects (median 103.4%), and recovery (median 48.9%).  Regarding use, this offers a labour-saving and cost effective, approach for high throughput analysis versus current protocols. We currently estimate that extraction costs can be reduced by >60% solely from the extraction cartridges and further still with analyst time saved (hours to ~20 minutes per sample).  We have also shown the potential for a mini-QuEChERS approach, offering improved extraction performance for all compounds studied (precision <20%RSD, matrix effects (median 103.9%), and recovery (median 53.2%)) and additional potential savings in production and customer purchase costs.  This, with the flexibility and translational nature of the technique, offers significant benefits for environmental analysis and an interesting sample preparation prospect for other matrices such as those encountered in clinical work.  

References
1.    Oxford English Dictionary. 3rd ed. Oxford: Oxford University Press; 2000 [cited 23 August 2018].  Available from: https://en.oxforddictionaries.com/definition/pollution 
2.    Department for Environment Food and Rural Affair (DEFRA). Waste water treatment in the United Kingdom – 2012. DEFRA. 2012. Report No.: PB13811.
3.    Prakash V, Bishwakarma MC, Chaudhary A, Cuthbert R, Dave R, Kulkarni M, Kumar S, Paudel K, Ranade S, Shringarpure R, Green RE. The population decline of Gyps Vultures in India and Nepal has slowed since veterinary use of diclofenac was banned. PLoS ONE. 2012; 7(11): e49118.
4.    Galligan TH, Amano T, Prakash VM, Kulkarni M, Shringarpure R, Prakash N, Ranade S, Green RE, Cuthbert RJ. Have population declines in Egyptian Vulture and Red-headed Vulture in India slowed since the 2006 ban on veterinary diclofenac? Bird Conservation International. 2014: 1-10.
5.    Kidd KA, Blanchfield PJ, Mills KH, Palace VP, Evans RE, Lazorchak JM, Flick RW. Collapse of a fish population after exposure to a synthetic estrogen.  Proceedings of the National Academy of Sciences (PNAS). 2007; 104 (21): 8897-8901.
6.    Anderson SE, Meade BJ.  Potential Health Effects Associated with Dermal Exposure to Occupational Chemicals. Environmental Health Insights. 2014; 8 (Suppl. 1): 51–62.
7.    Hahn S, Schneider K, Gartiser S, Heger W, Mangelsdorf I. Consumer exposure to biocides - identification of relevant sources and evaluation of possible health effect. Environmental Health, 2010; 9:7.
8.    Schweer C. Biocides – risks and alternatives. Challenges and perspectives regarding the handling of biocides in the EU. PAN Germany. 2010.
9.    https://www.ukwir.org/the-chemicals-investigation-programme-phase-2,-2015-2020
10.    Anastassiades, M., Lehotay, S. J., Štajnbaher, D., & Schenck, F. J. (2003). Fast and easy multiresidue method employing acetonitrile extraction/partitioning and “dispersive solid-phase extraction” for the determination of pesticide residues in produce. Journal of AOAC international, 86(2), 412-431.
11.    Matuszewski BK, Constanzer ML, Chavez-Eng CM. Strategies for the assessment of matrix effect in quantitative bioanalytical methods based on HPLC - MS/MS. Analytical Chemistry. 2003; 75 (13): 3019-3030.