A little more about our most commonly found chemicals
Many people look at our data and ask something like "Wow, that looks scary, but does this chemical actually do anything when it's at the concentration found in the Milwaukee or Kinnickinnick rivers?" That's a great question, and the answer depends on the chemical. Here we'll go through our most commonly found chemicals and explain what exactly the chemical us used for before it ends up in our water, as well as what the scientific literature says about toxic levels.
Caffeine is the most commonly detected PPCP in Milwaukee's waterways, as well as surface waters around the world (USGS). It is a naturally occurring chemical found in many natural products such as coffee and tea, and it is classified as a recreational drug due to its stimulant effect. While it is commonly found in our water, studies have shown it has minimal effect at the concentrations found in our samples. A common measure of toxicity is the "no-effect concentration" (NOEC). Caffeine's NOEC was determined using crustaceans and algae and found to be 5,200ng/L (Komori et al., 2013), which is more than 100x the median detected concentration in our data. However, there is minimal data that environmentally relevant concentrations (40.5ng/L) can decrease microbial respiration rates (Bunch et al., 2010).
Carbamazepine is a commonly used medication used to treat seizures and some types of pain. While the medication is commonly found in surface waters (USGS), it has little effect on the ecosystem at detected concentrations. The commonly used measure of toxicity, "predicted no-effect concentration" (PNEC), for carbamazepine is at least 420ng/L (Ferrari et al., 2003), which is more than 400x our median detected concentration for carbamazepine.
Sulfamethoxazole is an antibiotic medication used to treat bacterial infections. It was detected in about half of our samples, which is a similar frequency compared to national datasets; however, it was present at a lower median concentration (USGS). Another measure of toxicity is the effective concentration 50th percentile (EC50), or the concentration at which 50% of samples show an effect. For sulfamethoxazole this was found in microalgae and soil bacteria to be greater than 100,000ng/L (Bialk-Bielinska et al., 2011), which is orders of magnitude greater than the concentration found in our samples.
Atrazine is a pesticide which inhibits photosynthesis in certain types of plants. It is used in agriculture and gardening. It was found at a similar frequency but much lower concentration than at other surface water sites in the US (USGS). It has been found to inhibit some freshwater organisms, but it has no effect on the ecosystem at concentrations below 5,000ng/L (Solomon et al., 1996). Once again, this is much higher than the concentration found in our samples.
Trimethoprim is an antibiotic used to treat bacterial infections. As with many other chemicals discussed here, it was found at similar frequency but much lower concentration than in other rivers and streams (USGS). It has no effect on bacteria or algae until it is at a concentration millions of times greater than that found in our samples (Halling-Sorensen, 2000).
Benzoylecgonine is the main metabolite (breakdown product) of cocaine. There are few data on its detection frequency or concentration from the US, but a large study of several medium-sized Italian cities found it in every sample they tested, with a median concentration of 0.75ng/L (Zuccato et al., 2005). We found it in about a quarter of our samples at a median concentration of 2.11ng/L, so a little more than double that of the Italian study. Thankfully, however, the lowest reported concentration that exhibits a toxic effect is 500ng/L, at which it has been found to cause non-lethal oxidative stress to zebra mussels (Parolini and Binelli, 2013).
Triclocarban is an antibacterial compound was commonly used in soaps and lotions but was been banned by the FDA in 2016 (FDA, 2016). USGS did not collect data on triclocarban, but a large study conducted in Baltimore, MD, found a median concentration in surface water of 81ng/L, whereas the median detected concentration in our samples was 9.2. While it is similar to its chemical cousin triclosan in function, triclocarban is much less toxic to the environment. It has been shown to decrease sea urchin larval growth at concentrations as low as 640ng/L and can cause morphologic abnormalities in sea urchin larvae at 1,600ng/L (Torres et al., 2016).
Triclosan is similar to its chemical relative triclocarban and was a commonly used antibacterial chemical in soaps and lotions. However, in 2016 the FDA banned it along with triclocarban (FDA, 2016). While triclosan was present at a much lower frequency in our samples than in USGS samples, our detected concentration was significantly higher at 114ng/L (USGS). Unfortunately, multiple studies have shown triclosan can have significant toxic effects on the ecosystem (specifically, algae and frog tadpoles) at concentrations of 150ng/L and can change phytoplankton community composition at concentrations as low as 15ng/L (Veldhoen et al., 2006; Wilson et al., 2003). While triclosan is one of the few chemicals present in Milwaukee's waterways at a concentration high enough to have negative effects, due to the fact it was banned, there is hope it will dissipate and not be a problem in the future.
Thiabendazole is a medication used to treat fungal and parasitic infections in humans and animals. It was found at a smaller frequency and concentration than in the USGS study (USGS). There is little published literature to date on specific toxic levels, though it is of high concern due to its high solubility and ability to be absorbed by soil, thus enabling it to remain in the environment for long periods of time (Long et al., 2005).