Herbicides and pesticides, which for decades have been used without interruption in agriculture, are harmful not only to the soil, to plants and to the animals that feed on them, but also to dogs.

Many people also use these products to treat their home gardens and get rid of so-called weeds (wild plants often have considerable biological value, but that is another story).

A new study conducted by Angus Murphy, a plant scientist at the University of Maryland, has shown that herbicides can end up inside dogs' bodies — traces have in fact been found in the animals' urine.

Murphy and other scientists carried out a series of experiments to understand the effect and persistence of these products after application. They first sought to establish how long after application a herbicide can be picked up through incidental contact.

The researchers then applied the same quantity of three different types of herbicide to various plots of land, taking into account all the variables — for example, whether the grass was wet or whether the plants to which the product was applied were healthy or dying.

They then placed pieces of fabric on wooden blocks and dragged the blocks across the grass to determine how much herbicide they would absorb. The first test was carried out a couple of minutes after spraying, and was then repeated one hour, one day, two days and three days after the herbicide had been applied.

The results showed that two of the products tested on healthy grass can be accidentally "picked up" on the first day, but not beyond. The third herbicide, however, known as 2,4-D (dichlorophenoxyacetic acid), remained on the cloth for two full days after application. On dry lawns or lawns with unhealthy grass, the risk of picking it up through contact extended to three days.

To understand the actual impact on dogs, Murphy and his team recruited 33 dogs and their respective owners. Among these were some whose owners had sprayed herbicide on their lawns and others who had not. The researchers collected urine samples from the dogs both before and after the lawns had been treated with herbicides.

Most of the animals, including half of those whose owners had not treated their gardens, had herbicides in their urine. "Animals come into contact with herbicides — that is beyond doubt," Murphy said. "What surprised us most is that traces of these products were also found in the urine of dogs whose owners had not treated their own gardens."

The contamination therefore occurred during walks in surrounding green areas. The researchers are now trying to establish how much the pesticide residues found in dogs may harm them; in the meantime, they are calling on manufacturers to include specific recommendations on labels.