This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Two are better than one when it comes to sampling methods for tracking the location and timing of toxic chemical contamination in waterways, according to researchers at Penn State. The team tested two typical sampling approaches and found that both are needed to accurately assess the variety and concentration of contaminants of emerging concern—pharmaceuticals, personal care products, livestock manure-borne hormones, veterinary antibiotics and pesticides—in a watershed.
The team published their findings in the Journal of Natural Resources and Agricultural Ecosystems. "Even at trace levels, contaminants of emerging concern in surface waters can threaten aquatic organisms and human health," said study senior author and team leader Heather Preisendanz, professor of agricultural and biological engineering in the College of Agricultural Sciences. "This study addresses uncertainty about the occurrence, fate and transport of environmentally relevant concentrations of contaminants.
We wanted to determine the best way to detect trace amounts of chemicals in streams, so we could determine where and when those chemicals are entering a watershed." The researchers compared the results of grab sampling—collecting bottles of water at specific moments—to the results of sampling with polar organic chemical integrative samplers (POCIS)—devices left in the stream for days or weeks. Grab sampling, known as active sampling, reveals exactly what is in the stream at the instant the sample is taken—think of it like taking a snapshot, Preisendanz explained. In contrast, POCIS slowly absorb certain chemicals over time.
That passive-sampling method shows the average exposure during that period, more like a time-lapse composite image. The team has monitored five sites in the 24-square-mile (62-square-kilometer) Halfmoon Creek watershed, located in an agricultural area in central Pennsylvania, since 2021. For this study, they collected both types of samples from the five sites every two weeks during the 2023 and 2024 crop-growing seasons, May through September.
The five sites were arranged in a nested watershed design, meaning they were placed at key locations to help researchers understand how contaminants varied across different sections and tributaries in the watershed. The nested design allowed the researchers to better understand how well each sampling method was able to capture spatial and temporal—space and time—patterns of where contaminants occur and how concentrations change over time. It also helped them learn how the long-term averages measured by POCIS compared with the instantaneous measurements from grab samples.
In addition, monitoring multiple locations helped identify "hotspots." Because the researchers sampled five sites instead of just one at the watershed outlet, they could identify parts of the watershed where contaminant levels were consistently higher. These hotspots may indicate nearby pollution sources, such as agricultural fields or wastewater inputs, Preisendanz said. While each method captured contaminants—most commonly the herbicides atrazine and simazine, the insecticide clothianidin and the stimulant caffeine, with each appearing in at least 68% of samples collected by both methods—each method also missed significant information.
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