Instrumentation and Research Allow Lower Detection of Tetracycline Antibiotics
By Steve Ress
State of the art equipment and dedicated research has allowed the UNL Water Sciences Laboratory (WSL) to find traces of tetracycline antibiotics as low as 0.5 parts per billion (ppb) in soil and as low as 0.01 ppb in groundwater.
“The new equipment has enabled us to develop a new method for analysis of tetracyclines and some of their metabolites in water that is five to 20 times more sensitive than our previous method,” said research chemist Dan Snow, who manages the WSL.
Tetracyclines are a group of antibiotics used for treating infection and disease in both humans and animals. Discovered in the 1940’s and 50’s, they were later found to have a profound effect on livestock growth rates. By the 1990’s estimates are that more than 10,000 tons of antibiotics were administered to animals annually in the U.S., with tetracyclines comprising roughly one-fifth of that total.
After given to an animal in feed, water, or by injection, they eventually are excreted either unchanged or in a metabolized, or modified, form.
“Tetracyclines and other antibiotics given to livestock can be excreted in manure and then, depending on how that waste is handled, can end up in feedlots, lagoons, fields, and run-off to streams and lakes.” Snow said.
Because of their widespread use in medicine, it is believed that many bacteria have become resistant to their effects, rendering these drugs ineffective in treating illness or infections. Since the same drugs are administered to animals, this is a way antibiotics can get into the environment and another avenue for proliferation of antibiotic resistance. Because of the concerns for antibiotic resistance, it is very important to have accurate information regarding the occurrence of these compounds in the environment. Improved detection of tetracyclines at low levels in water and soil is necessary to understand their occurrence and assess whether there is a problem.
“The levels of tetracycline found in the environment are not normally toxic to humans or animals, but their presence at low levels in water and soils could contribute to the increase in antibiotic-resistant bacteria,” Snow said.
“Because we are only now beginning to study tetracyclines in the environment, we don’t really know whether they can get into groundwater. Initial tests suggest they largely remain bound to soil particles,” he said. That makes the new, lower detection limits the WSL can test to even more important.
In the late 1990’s, staff at the lab developed a method to concentrate and analyze tetracyclines in water with an instrument called an ion trap mass spectrometer. The results of these early tests indicated that groundwater samples impacted by livestock wastewater lagoons in Nebraska did not have detectable levels of tetracyclines (greater than 2 ppb), despite the fact that 85 percent of the lagoons studied showed levels of the antibiotic ranging from 10 to 10,000 pbb. This methodology was published in the Journal of Chromatography in 2001.
These results led Snow and fellow UNL researchers Jose Payero and David Tarkalson at UNL’s West Central Research and Extension Center in North Platte to begin investigating whether tetracyclines in cattle manure applied to irrigated corn might end up in ground water or be held in the soil.
“The results from the ion trap showed low levels of tetracycline in manure-treated soil, but the concentrations were highly variable even from similar samples. We needed an instrument that could provide more accurate results in environmental samples,” Snow said.
The need for improved detection of these and other pharmaceutical compounds lead to the acquisition of a triple quadrupole mass spectrometer last year.
While the ion trap is a highly sensitive and versatile instrument for analysis of pharmaceutical compounds like antibiotics, the “triple quad” provides superior sensitivity and greatly improved detection mainly because of the way the chemicals are separated and detected.
The availability of both the ion trap and triple quad systems provides nearly unlimited capabilities for study of new types of contaminants like pharmaceuticals in the environment.
Using the new equipment and methodologies, the lab can detect tetracyclines to about 0.01 ppb in water and as low as 0.5 ppb in soil. This combination of equipment and methodology allows the three UNL researchers to hone their initial study of where the tetracycline in manure used on cornfields may wind-up and whether it could pose a potential health risk to humans and animals.
“Researchers in Nebraska are extremely fortunate to have this type of instrumentation available. There are only a handful of universities in the world with this capability dedicated to water research.”
The UNL Water Sciences Laboratory is part of the UNL Water Center and School of Natural Resources. The U.S. Environmental Protection Agency helps fund this research.
