Contaminant mixture dynamics and fate in an effluent dominated stream

Thousands of chemicals are released into streams and rivers from wastewater treatment plants. Wastewater treatment plants (or WWTPs) are only legally required to remove contaminants nutrients, heat, and bacteria from household wastewater. Many WWTPs release the treated water into small streams and creeks, meaning that most of the water downstream of the WWTP is made up of treated wastewater effluent. These small streams, called effluent-dominated streams are often full of thousands of man-made chemicals. The chemicals from the WWTP (like pharmaceuticals) and chemicals from other sources (like runoff from cropland, neighborhoods, streets) mix together in these effluent-dominated streams, and they create potentially toxic mixtures in the environment. These mixtures can affect wildlife and people as they flow downstream. My research aims to study these mixtures in surface water, groundwater, and in the broader ecosystem. To do this, I completed three studies at Muddy Creek, which is an effluent dominated stream located in Coralville, IA.

In my first study, I measured 17 different insecticides and pharmaceuticals in surface water and wildlife (fish, aquatic insects, spiders) in the effluent-dominated stream. I measured two neonicotinoids (a class of insecticides known to kill honeybees), imidacloprid and clothianidin, in the spiders living next to the stream. I also measured multiple pharmaceuticals in the fish and in the aquatic insects. This shows that these chemicals can move from the wastewater to aquatic animals and up the food chain into land-based animals.

In my second study, I measured the mixtures of chemicals in the surface water using state-of-the-art instrumentation. The method I used is called non-target analysis, which means that I can analyze a sample for thousands of chemicals at a time. Normally, I can only measure up to 100 chemicals at a time with standard instrumentation. Here, I re-analyzed saved samples from previous studies. The samples were previously measured for 154 chemicals, and with my new methods I found 20 times more chemicals in the same surface water samples. I also identified groups of new chemicals in the stream where the WWTP water first mixes with the stream water. This suggests that new chemicals formed quickly in the stream, which is concerning because many of the chemicals do not have names, and their toxicity is unknown. I also identified 8 hormone disrupting chemicals upstream of the WWTP that were previously overlooked. My findings here have important implications for impacted ecosystems and downstream communities that inadvertently have wastewater in their drinking water source.

In my last study, I measured contaminants in both the surface water and groundwater of Muddy Creek. My goal was to understand if the sediments in the bed of Muddy Creek are increasing or decreasing the concentration of chemicals as they flow away from the WWTP. I analyzed the samples for chemicals including ions, pharmaceuticals, industrial products, pesticides, and forever chemicals (PFAS). I also used non-target methods, like in my last study, to identify patterns in the pollution. In the surface water, the surface water results showed that the chemical mixtures in the stream never return to natural conditions after the WWTP effluent is added. I also identified two PFAS chemicals at the same concentration in all samples. These findings highlight the vulnerability of shallow aquifers, which are more susceptible to upstream effluent contamination than previously thought, posing risks for downstream communities relying on surface water and shallow groundwater as their drinking water sources.