UNL scientists analyze chemical data, point to environmental concerns regarding AltEn wastewater spill

By: Geitner Simmons, IANR Communications

University of Nebraska-Lincoln scientists have conducted extensive analysis of the pesticides, fungicides and related chemicals released in a major wastewater spill from the AltEn ethanol plant near Mead, Neb., in February 2021. Their analysis covers a six-month period of surface water sampling and provides detailed findings on the presence of the chemicals not only on the AltEn site but also on land in the surrounding area receiving application of AltEn waste products. A particular concern is the potential long-term environmental threat from byproducts created by the degradation of chemicals contained in the samples, UNL scientists said.

The toxicity specifics of the pesticides (including imidacloprid, thiamethoxam and clothianidin) are long established. But scientific understanding is not well established of the environmental and health threats from the pesticides’ degradation byproducts (including imidacloprid-desnitro, imidacloprid-urea and thiamethoxam urea) found at the sampled areas.

The UNL analysis says environmental monitoring indicates “continual detection” of imidacloprid-desnitro, for example, which “suggests that this compound is persistent.”

The Claire M. Hubbard Foundation funded the analysis through a gift to the University of Nebraska Medical Center College of Public Health.

For its ethanol production, the now-closed AltEn plant used pesticide- and fungicide-treated seed corn rather than harvested seed. In the February 2021 spill, a frozen pipe under a four-million-gallon storage tank broke. The discharge, containing manure and an ethanol byproduct known as thin stillage, traveled more than four miles from the site. In addition, solid waste, known as wetcake, and wastewater were applied to surrounding cropland in Saunders County in 2018 and 2019, increasing the extent of the affected area.

UNL scientists monitored the discharges along two surface water routes near the AltEn property, beginning in April 2021. Some April water samples containing the pesticides imidacloprid, thiamethoxam and clothianidin, as well as their degradation compounds, exceeded the research-determined levels for chronic or acute toxic threats to aquatic organisms. Concentrations of imidacloprid and thiamethoxam in subsequent months fell below established toxic thresholds. But, UNL scientists said, that does not necessarily remove environmental and health concerns because some detected transformation products of these pesticides were found to increase with time.

Water samples containing the pesticide clothianidin declined over time in terms of the toxicity threat but remained “significantly higher than the EPA exposure benchmarks,” the UNL analysis said. “Clothianidin’s major risk concern is to nontarget insects, especially honey bees.”

Although the April levels for three fungicides (azoxystrobin, picoxystrobin and pyraclostrobin) did not exceed established toxicity levels, UNL researchers expressed concern about possible effects from the long-term persistence of the fungicides. In regard to picoxystrobin, for example, the UNL analysis states that on both surface water pathways studied, “the concentrations never reached the benchmarks set by EPA. However, due to the known health hazards of this fungicide, its chronic presence in the environment is concerning.”

The analysis offers similar conclusions regarding azoxystrobin, a fungicide posing a high toxicity threat to freshwater fish and freshwater invertebrates: “Although the detected values from grab samples are negligible compared to all the EPA benchmarks for fish and invertebrates at all locations, the longtime presence of this fungicide could pose a threat to the exposed fish and invertebrates.”

The coauthors of the new UNL report are Daniel D. Snow, director of UNL’s Water Science Laboratory at the Nebraska Water Center; Shannon L. Bartelt-Hunt, the Donald R. Voelte Jr. and Nancy A. Keegan chair of engineering with the Department of Civil and Environmental Engineering and a fellow at NU’s Daugherty Water for Food Global Institute; postdoctoral associate Shahab Karimifard; Seth Caines, a junior majoring in environmental engineering; and Patrick Nityitugize, a senior majoring in integrated sciences.

In follow-up to the study, UNL researchers will integrate their water-sampling results with data from sampling devices that accumulate chemicals over time to identify chemicals that may be present at lower levels in the environment. In addition, they will compile historical site data including data obtained from the state Department of Environment and Energy. Scientists with the U.S. Geological Survey and the Environmental Protection Agency also will be involved in follow-up work. EPA scientists plan to evaluate the effects of high levels of these chemicals to local bee populations and measure occurrence of other degradation products in water and soil samples. The USGS investigators are focusing their efforts on understanding the long-term consequences of the elevated concentrations of these compounds to aquatic life and monitoring their occurrence in local groundwater.