Tracking Manure-Borne Pathogens
To study runoff of disease-causing microbes, Beltsville scientist use this
rainfall simulator designed and constructed by microbiologist Daniel Shelton
(right) and instrument maker Paul Balsley.
Two self-contained artificial hills in Beltsville, Maryland, may yield some
answers about one path that microbial pathogens can take to taint food and
water supplies. Scientists with the Agricultural Research Service want their
study, begun this year, to lead to better ways for dairy and beef farmers to
ARS is conducting the study because research has shown that use of manure as
a natural fertilizer on pastures and fields is one way that microbial pathogens
are spread in the environment, says microbiologist Daniel R. Shelton. He is
with the ARS Environmental Chemistry Laboratory at Beltsville.
"The experiments are part of a broader food safety and water quality
project that began in 1996 and has recently been expanded to include several
labs throughout ARS," says Shelton. He and Beltsville colleagues are
focusing on the protozoan Cryptosporidium parvum and the bacterium
Escherichia coli O157:H7.
C. parvum sickened more than 400,000 people in Milwaukee,
Wisconsin, in 1993. The protozoan lays eggs, or oocysts, inside intestines of
domestic and wild animals and humans. Shed from manure or human waste,
disease-causing oocysts can enter lakes and streams by rain or snowmelt runoff
and from inadequate septic systems.
E. coli O157:H7 contamination of meat and produce has caused
several well-known outbreaks in recent years. The bacteria can occur in
manureas well as at many other points in the food-supply chain, from the
farm to the meal table.
Field lysimeters with different slopes10 percent (foreground) and 20
percent (background)allow scientist to study microbial transport at
different flow rates.
The two moundsabout 40 feet wide by 70 feet long and 15 feet
highare called soil lysimeters. Lined with plastic to keep soil water
from leaching in or out, they allow scientists to study the movement of soil
water and possible contaminants down the sides, or width, of the slope.
The two lysimeters are among six at Beltsville. One in the new study has a
10-percent slope on each side; the other, 20-percent.
Both mounds have sandy soil on one side and heavier loam on the other,
allowing movement in two soil types to be evaluated at once. A rainfall
simulator lets scientists regulate precipitation.
The lysimeters are above the water table, and gutters around them channel
runoff water to storage tanks. "This design allows us to safely study the
parasites without fear of their escaping," says Shelton.
Last year, he planted orchardgrass on the mounds to simulate pasture. This
year, he will study only soil water movement. Next year, he plans to add
oocysts to manure he will apply on the mounds. As a stand-in for pathogenic
E. coli O157:H7, he'll trace benign strains of E. coli.
Shelton says the lysimeter study is a prelude to watershed-scale studies on
Beltsville fields and a Pennsylvania dairy farm. He also plans to modify two
other Beltsville mounds to see how well grass strips might filter out
pathogens.By Don Comis,
Agricultural Research Service Information Staff.
This research is part of Food Safety (#108), an ARS National Program
described on the World Wide Web at
and of Water Quality and Management (#201), described at
Daniel R. Shelton is in
the USDA-ARS Environmental Chemistry
Laboratory, Bldg. 001, 10300 Baltimore Ave., Beltsville, MD 20705-2350;
phone (301) 504-6582, fax (301) 504-7976.
"Tracking Manure-Borne Pathogens" was published in the
November 1999 issue of
Agricultural Research magazine.