As we spew increasingly varied chemicals into the environment, the ability to detect contaminants in water is becoming a task more vital than ever. But, as we move towards systems toxicology to give a multi-faceted view of the damage contaminants can do, will chemical analysis be enough?
Research scientists, government agencies, and corporate entities around the world are desperately seeking ways to identify unknown and emerging chemical contaminants in the water supply – and determine what risk they may pose to our health.
To that end, environmental labs are using advanced chromatography, spectrometry, and other technologies to detect trace levels of a growing list of emerging contaminants, such as hormones that can make fish grow to twice their normal size or give them a mix of male and female characteristics.
Contaminants of emerging concern, or CECs, include pharmaceuticals, personal care products (including ingredients in products ranging from mouthwash to antibacterial soap), and various perfluorinated compounds that are showing up in the world’s rivers, lakes, and groundwater with increasing frequency.
The effect of long-term exposure of CECs on humans is not yet known, but we do know that population growth and urbanization, coupled with dramatic shifts in precipitation, have caused extreme water stress and forced us to explore alternative water resources. A key example is drought-prone California, where the governor has mandated the development of uniform water recycling criteria for direct potable re-use. This process involves directly treating municipal wastewater to a high enough standard for use as drinking water.
However, expert panels within the State of California, the US Environmental Protection Agency, the World Health Organization, and other bodies have concluded that the current approach for assessing water safety from chemical analysis alone may be insufficient to protect the environment and public health.
Environmental analysis needs to be performed faster, more reliably, more efficiently, and with higher quality results than ever before. Unfortunately, pharmaceuticals, personal care products, pesticides, perfluorinated compounds and other potentially toxic chemicals can be difficult to detect in environmental and biological matrices. Furthermore, there is a plethora of as yet unidentified chemicals that co-exist in these samples that could contribute to adverse health outcomes. Numerous expert panels and regulatory agencies agree that water safety will require extensive monitoring to address cumulative chemical toxicity and to look for new chemical contaminants using nontargeted analyses.
With high-resolution accurate mass spectrometry, researchers can detect known contaminants (those included on regulatory and target lists), suspects (structural or spectral information appearing in databases), and unknowns (chemicals that require structural elucidation through fragment analysis).
Unfortunately, a sample-by-sample analysis for all emerging contaminants is an exceptionally unwieldy task, given the large number of chemicals commercially available, along with their degradation and transformation products, which result from environmental exposure and treatment, purification, and disinfection processes.
Best of both
A new approach combines analytical chemistry and rapid biological screening by which labs can identify the chemical content of water samples along with biological toxicity and assess the risks or verify safety. Currently, the links between environmental analytical chemistry technologies and life science technologies are somewhat limited. In vitro
assays applied to environmental monitoring generally use engineered reporter gene technologies and rely on a single gene expression per experiment. Similarly, these assays can also involve living cells, developing larvae, or live animals that demonstrate changes to physiological, biochemical, or oxidative behaviors when exposed to chemical contaminants.
Changes to the biological system following exposure identifies specific samples which are then evaluated for chemicals of interest to assess the risk and the possible need for exposure limits. This effect-driven identification of chemical activity categorises samples that should undergo nontargeted screening analysis to identify the offending chemical or chemicals. Using iterative chemical fractionation and nontargeted high-resolution accurate mass spectrometry to analyse “active” samples would identify chemical structures responsible for eliciting the biological response.
Every day, scientists identify new and emerging chemical compounds in environmental matrices requiring further investigation into the effect these toxicants have on humans and biota. Understanding the biochemical and physiological impact of chemical exposure allows researchers, regulators, and manufacturers to determine the potential toxicity of newly developed chemicals as well as recently identified emerging chemical contaminants.
As noted, one of the ways they do this further investigation is through in vivo biological research: exposing live animals, developing larvae, or cells to extracted water samples of interest. When they see changes to cell metabolism, morphology, mortality, or other chemotoxic affects, further analysis of the water extract is required to identify the chemical constituents.
Identifying the biological processes that are regulated, up or down, in response to chemical exposure requires research into metabolic pathways, gene expression and transcription, protein synthesis, and so on. In vitro exposure research using arrays that consist of subcellular systems or whole tissues allows scientists to quickly identify affected processes and classify the exposure risks. Understanding this risk allows regulatory agencies to protect the public by developing new monitoring and compliance requirements or updating existing ones to reflect changes to the maximum permissible levels of chemical release.
Suspect and nontargeted screening
For nontargeted screening and in vitro
applications, researchers need sophisticated tools to identify the toxicants and their impact on biochemical and physiological processes. They must be able to monitor cell metabolism to quickly and efficiently identify chemicals that pose a potential risk. High-resolution mass spectrometry delivers the selectivity and sensitivity required to detect new chemical toxicants, in situ degradation or transformation products, and biochemical metabolites. Then, specialised software can facilitate chemical identification and provide a map to potential metabolic transformation in vivo
Successful effect-driven characterisation of the most biologically and chemically relevant contaminants requires suspect and nontargeted screening, preferably using tools that reduce false positives without compromising data quality and spectral resolution.
Measuring what's important
With over 20,000 genes, 200,000 proteins, and thousands of pathways, it is not possible to measure everything in a cell at once, but it is possible to measure what provides the energy that drives them – metabolism.
Using label-free extracellular flux (XF) technology, researchers can see, in real time, how a live cell is functioning – and how introducing a specific chemical may impact it. By measuring several metabolic parameters and functions they can detect discrete changes in cell bioenergetics, which gives them a window into the critical functions driving cell signaling, proliferation, activation, toxicity, and biosynthesis.
In short, XF technology enables scientists to research the role of cell metabolism in toxicology. It empowers them to move beyond analysing what the cells are, and reveal a clearer picture of what they do.
Identifying and assessing unknown contaminants in the water supply is clearly a complex challenge, one that requires us to harness all the tools at our disposal. Indeed, scientists are combining analytical products from across the four major omics (genomics, transcriptomics, proteomics, and metabolomics) into an integrated approach known as systems toxicology to identify toxicologically relevant chemicals in the environment. This approach links exposures to outcome-specific patterns obtained from multiple omics profiles to gain a deeper understanding of biological processes. By integrating multi-omic data sets, we are better able to identify toxicity pathways, modes of action, mechanisms of disease, and biomarkers of toxicity.
Craig Marvin is the Global Environmental Industry Manager at Agilent Technologies