Soil activity able to offset antibiotic residue fears

Tests show soil microbes help prevent uptake of antibiotics in food crops

LONDON, Ont. —Spreading municipal bio-solids on farmland comes with risks, but bio-solids also alleviate the risk by stimulating soil life, according to an Agriculture Canada scientist.


Ed Topp, a researcher at the Southern Crop Protection and Food Research Centre in London, said most micro-pollutants such as path-ogenic bacteria and antibiotics are broken down by soil microbes.


“When bio-solids are added to the soil we found enhanced feeding activity, not just in the year they were added but for at least four years after,” Topp said.


“We counted the number of earthworms and you can see the number were much higher with the bio-solids than in the control.”


He said 120,000 dry tonnes of municipal bio-solids are spread annually on Ontario farmland.


“In Ontario, you can use it on vegetable ground, but you need to wait a year between the application and harvest.”


Topp sees the regulation as a reasonable approach, but suspects most farmers growing crops for human consumption avoid using bio-solids. There’s a stigma among consumers when it comes to municipal sewage.


Topp and his team will take a closer look at municipal bio-solids this summer, comparing three types that are applied to Ontario farmland: heat treated and pelletized; aerobically digested and dried; and anaerobically digested and de-watered.


“We want to see if one type is better than the others as far as what ends up in the soil and what might be taken up by the crop,” he said.


“There is pressure to recycle various organic amendments. It’s the most economical way to recycle nutrients while improving soil quality. We and our collaborators want to ensure the science validates the safety of this practice.”


The work includes evaluating the antibiotics that find their way into municipal wastes. The concern is that the antibiotics can be taken up by food crops and increase anti-biotic resistant bacteria.


Laboratory experiments have show this can occur, but thanks to soil microbial activity, crops are unlikely to take up antibiotics when normal farm practices are used.


In earlier work involving livestock manure, Topp found the soil ecosystem increases its capacity to break down antibiotics with repeated applications.


“We’re doing the same kind of work with this project, but we’re using human manure.”


The environment is one area in which antibiotic resistance in bacteria can be developed. The others are related to the over prescription of antibiotics for people and livestock.


“Governments are trying to devise policies to combat the overuse of antibiotics in people,” Topp said.


“It’s clearly a problem, and the Canadian Veterinary Association is encouraging the prudent use of antibiotics.”


The Water Environmental Association of Ontario recently presented Topp and his team with an Exemplary Bio-solids Management Award.