How many contaminants of emerging concern (CEC) can you assess from one set of mussels? Turns out if SGS AXYS is doing the measurement, it’s at least 330! Scientists Andrew James, Jennifer Lanksbury, Tarang Khangaonkar and James West from the University of Washington Tacoma, Washington Department of Fish and Wildlife, and Pacific Northwest National Laboratories evaluated the exposure of bay mussels (Mytilus Trossulus) in the Puget watershed to CEC through sampling and hydrodynamic modeling. Results from this study were published recently in the Science of the Total Environment (West et al. 2020).

Mussels are a reliable monitor of contaminant exposure as they are filter feeders, process large amounts of water and accumulate contaminants due to their inability to metabolize many chemistries. Think of them as a biological time-integrated sampler. They continue to be used in multiple contaminant monitoring programs including NOAA’s Musselwatch which SGS AXYS has supported with POPs and CEC analysis for many years now.

Study Objectives and Methods

1. To “provide the first systematic survey of CECs in Puget Sound biota” in multiple locations
2. Compare results to output from a hydrodynamic transport model to study the use of modelling for estuary-scale exposure prediction

Scientists deployed caged mussels in 18 locations through the Puget Sound for two months. SGS AXYS analyzed 330 different CECs for this project in composite mussel samples. These are all targeted, multi-contaminant GC or LC-MS/MS methods that use isotope dilution and other best practices to maximize data quality. This work continues our long history of measuring contaminants in the Puget sound, published previously by Long et al., 2013; Meador et al., 2016.

• 231 PPCPs of diverse chemistries
• 13 PFAS including PFOS and PFOA
• 82 pesticides
• Surfactants nonylphenols and ethoxylates. – Still widely used as surfactants in many products.

Scientists then used hydrodynamic models simulating both wastewater treatment plant inputs and stormwater runoff to understand contaminant sources.

Results

Study takeaway on CEC occurrence:

“Frequently detected chemical classes included alkylphenol ethoxylates (APEs), antibiotics, central nervous system agents, and the chemotherapy drug melphalan. Three compounds, 4-nonylphenol (4-NP), virginiamycin M1, and sertraline were detected at all 18 locations. Less frequently detected classes included other pharmaceuticals compounds, metabolic regulators, current-use pesticides, and DEET. The hormone drospirenone, the industrial chemical octachlorostyrene, and the surfactant perfluorooctanesulfonamide (PFOSA) were each detected at one location.

While concentrations were low, the main concern here is additive and synergistic effects caused by low-level chronic exposure.

Alkylphenols

The detection of alkylphenols in these mussels is consistent with results found in shellfish in multiple locations and is continuing evidence of the issues posed by these surfactants, which can show endocrine disrupting potential at concentrations close to 1 µg/L. Concentrations in these mussels were significantly lower.

Antibiotics

Virginiamycin is an antibiotic frequently used as a growth promoted for livestock, and is also naturally occurring. Other antibiotics were also detected in multiple samples, which is of concern due to the promotion of antibiotic resistance.

SSRIs and CNS agents

Selective serotonin reuptake inhibitors ((SSRIs) such as sertraline were also detected in the samples. Sertraline (original brand name Zoloft) is among the most prescribed anti-depression drugs in the US and their detection in mussels is good indication of this use pattern. Oxycodone, an opioid of much current focus, was also detected in some of the samples.

Other PPCPs

In addition, melphalan, a widely used chemotherapy drug, iopamidol, a ubiquitous X-Ray contrast agent, and metformin, an antidiabetic drug were detected. With melphalan, the measured concentrations were within a factor of two of estimated therapeutic doses in cancer patients. The authors state that

The widespread occurrence, exposure potential, the biologically active nature of this chemotherapy drug indicates that melphalan should be considered a priority compound for further monitoring.

PFAS

This study confirmed with very low PFAS incidence that mussels are not a good indicator for PFAS due to their ability to express transporter proteins and clear them from their systems swiftly.

Hydrodynamic Modeling

The modeling results showed multiple sources contributing to CEC burdens in the mussels. Stormwater runoff contributed most the alkylphenol concentrations from urban centres. For many other CEC including pharmaceuticals, proximity to wastewater treatment plants increased detect frequencies of PPCPs.

Summary

“In general, it appears that mussels in the Puget Sound nearshore were exposed to a wide range of CECs at low concentrations, though some may be at levels of biological concern.”

Overall, this is a very interesting study combining the use of mussels as biological indicators, comprehensive CEC analytical methods, and hydrodynamic modelling to understand sources and inputs,