By Abigail Joyce and Mallory Pirogovsky
Originally published at ScientificAmerican.com
Hydrophobic organic compounds are often introduced into aquatic environments through manufacturing and sewage discharge, storm water runoff, and by leaching out of consumer waste. The hydrophobic nature of these compounds allows them to concentrate in the sediment. Once in the sediment, compounds can be broken down or re-suspended into the water column. Accumulation of these compounds in addition to legacy compounds existing in the environment from previous use (e.g. polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs) and DDT) can lead to lasting ecological effects and possible toxicological effects on local fauna and humans. Contaminants of emerging concern (CECs) include: pesticides, insecticides, herbicides, pharmaceuticals and other personal care products, flame retardants, and DDT metabolites.
There are currently gaps in our knowledge of occurrence, fate, and health hazards of many CECs. Assessing the risks they pose to the environment and human health is essential so that regional monitoring and regulation can be effective. Measuring aqueous concentrations of CECs can provide perspective on the effectiveness of reducing emissions and lowering of exposure, and can be linked to bioaccumulation and biomagnification risks in the food chain. However, because many of these chemicals are hydrophobic, their aqueous concentrations are low (generally at a sub ng/L concentration). These low concentrations make targeting and quantifying CECs a challenge.
Traditionally aqueous concentrations have been monitored by extracting large volumes of water or by measuring bioaccumulation in aquatic animals (i.e. bi-valves). Large water extractions generally have a larger (less favorable) detection limit and are very labor intensive. When monitoring aquatic animals it is difficult to determine a dissolved water concentration; furthermore it is difficult to make comparisons between different environments, as different environments support different species.
In the early 1990’s passive sampling was introduced as an alternative for quantifying dissolved hydrophobic organic compounds in aquatic media. Passive sampling is a simple, low cost, no power, unattended method that concentrates analytes in a collecting medium from a sampling medium as a result of differences in chemical potentials. Two main types of passive samplers became popular: solid phase microextraction (SPME) and semi-permeable membrane devices (SPMD).
SPME is comprised of a polymer coating fused to a silica fiber that can be directly injected into a GC port, eliminating all need for additional lab work up. Many different types of sorbent coatings have been developed making it available for monitoring a diverse amount of CECs. They are limited in their ability to be analyzed, and because of the small fibers they have relatively high detection limits and can be fragile.
SPMD is a low-density polyethylene tube filled with a lipophilic reservoir (e.g. triolein). These samplers require careful work up of the lipophilic reservoir and polyethylene tubing and are also prone to biofouling and can tear easily, but offer lower detection limits for many hydrophobic compounds. Passive samplers are typically operated in the equilibrium measurement mode, resulting in a time integrated estimate of dissolved HOC concentration over an extended time– which can take up to months.
A new, simpler variation of the SPMD employs just the polyethylene (PE) cut into strips, which maintains the low detection limits of the SPMD, while creating a more rugged sampler than SPME and SPMD. PE has shown to be as efficient as SPMDs in sampling HOCs. However, PE is limited to polyethylene as a sorptive medium, narrowing amount of CECs that can be targeted. It also requires an in-lab work up. This work up however allows for each sample to be analyzed several times if needed.
Passive samplers have the potential to replace high volume water extraction and aquatic species bioaccumulation for the monitoring of CEC’s in marine environments. Environmental groups like National Oceanic and Atmospheric Administration (NOAA) collect mussels for their Mussel Watch project, which is an ongoing monitoring program at over 300 sites covering 140 different compounds. Programs like mussel watch collect mussels from coastal sites where these mussels grow naturally. These programs give good insight into a compound’s bioavailability and range but the results do not translate into water column concentrations and is limited to coastal areas where mussels reside.
A passive sampler monitoring study has no limits on where it can be done, and water column concentrations can be determined. Our passive sampler study was carried out jointing between USC Dornsife, Southern California Coastal Water Research Project (SCCWRP), and Loyola Marymount University using both PE and SPME passive samplers. With funding from SeaGrant the goal of the sudy was to determine the water concentration of several CECs. The chosen CECs included two metabolites of the legacy pollutant DDT (DDMU and DDNU), two flame retardants (BDE-47 and TBPH), two banned industrial chemicals (PCB 8 and 209), and one current use pesticide (Methoprene).
Two prominent features within the Southern California Bight are Santa Monica Bay and the Port of Los Angeles (LA Harbor). Along with urban runoff both Santa Monica Bay and Los Angeles harbor receive treated wastewater effluent. Hyperion water treatment plant located in Playa Del Ray has been in operation since 1894 when it began discharging into Santa Monica Bay. In contrast to the municipal water that Hyperion collects and treats, the Terminal Island water treatment plant collects and treats water from the heavily industrial LA harbor area. Located 20 miles south of Los Angeles in San Pedro, the Terminal Island discharge point is within LA Harbor roughly 275 m from the shore.
In summer of 2011 passive samplers (both PE and SPME) were deployed at both Hyperion and Terminal Island receiving sites at varying depths and distances from the primary output location. SPME fibers were encased in copper housings to protect the fibers and ward off biofouling. PE was deployed on copper wire rings and in copper housing. In order to compare these passive samplers’ uptake to the traditional mussel monitoring, live caged mussels were deployed alongside the passive samplers. Deployments and retrievals were done by boat both in the harbor and the bay. Passive samplers were retrieved after 29 days, and mussels were retrieved after 90 days. Results from this study are in the process of being published.
Results from this study will provide many facets of information: comparison of not only passive sampler uptake to live mussel uptake, but also uptake differences between passive samplers, how depth plays a role in the water column concentration, as well as whether proximity to the outfalls affects concentrations will also be examined. Furthermore the concentrations of the targeted CECs will be determined.
About the Authors:Mallory Pirogovsky (left) and Abigail Joyce (right) are both Ph.D. students in the Department of Chemistry in the USC Dana and David Dornsife College of Letters, Arts and Sciences, and are planning on graduating next spring using results from this experiment to support their thesis work.
Editor’s note: Scientific Research Diving at USC Dornsife is offered as part of an experiential summer program offered to undergraduate students of the USC Dana and David Dornsife College of Letters, Arts and Sciences. This course takes place on location at the USC Wrigley Marine Science Center on Catalina Island and throughout Micronesia. Students investigate important environmental issues such as ecologically sustainable development, fisheries management, protected-area planning and assessment, and human health issues. During the course of the program, the student team will dive and collect data to support conservation and management strategies to protect the fragile coral reefs of Guam and Palau in Micronesia.
Instructors for the course include Jim Haw, Director of the Environmental Studies Program in USC Dornsife, Assistant Professor of Environmental Studies David Ginsburg, SCUBA instructor and volunteer in the USC Scientific Diving Program Tom Carr and USC Dive Safety Officer Gerry Smith of the USC Wrigley Institute for Environmental Studies.