Pesticides in rivers | The scourge runs its course

They are hardly used anymore, but their legacy lives on in the environment. Neonicotinoids continue to be detected at levels harmful to aquatic organisms, reveals a report from the Quebec Ministry of the Environment.

Daphne Cameron
The Press

Less used, still threatening

Despite a dramatic drop in their use, neonicotinoid pesticides are still measured in agricultural rivers at concentrations that threaten aquatic life.

This is revealed by a report on the presence of pesticides in water in Quebec, published discreetly on the website of the Quebec Ministry of the Environment and the Fight against Climate Change (MELCC).

Better known as “bee-killing” pesticides, “neonics” are a family of insecticides that can also have harmful effects on aquatic invertebrates when they leach from fields into waterways.

Since 1992, the Department has documented the presence of pesticides in agricultural areas dominated by corn and soybean monocultures, by taking samples from four control rivers.

The report, which covers the period 2018 to 2020, is the first update since farmers were required to obtain a prescription from an agronomist to buy and plant seeds coated with neonicotinoids.

Because since 2018, three neonicotinoids – clothianidin, thiamethoxam and imidacloprid – have been on the list of the five pesticides most “at risk” of causing damage, according to the Quebec government.

Maximum threshold exceeded most of the time

The good news: in the four barometer rivers, neonicotinoids are now detected less frequently and in lower concentrations. The problem is that, on average, the samples still exceed most of the time the “chronic aquatic life criterion” (CVAC), that is to say the maximum threshold of a product at which the Aquatic organisms can be exposed for their entire lifetime without adverse effects.

In theory, the most vulnerable species such as aquatic invertebrates can tolerate a maximum exposure of four days at “chronic” thresholds; beyond that there will be damage.

“We can be happy to have controlled neonicotinoids, we can be happy that the frequencies of CVAC overruns are decreasing, but can we really be happy that there are still overruns? », underlines Louise Hénault-Ethier, director of the Center Eau Terre Environnement of the National Institute of Scientific Research.

“It looks benign, but aquatic invertebrates, the whole food chain depends on them,” adds Sébastien Sauvé, professor of environmental chemistry at the University of Montreal.

“The problem with neonics is that it’s very toxic to aquatic invertebrates. If we remove them, all the small fish no longer have invertebrates to eat and the big fish that ate the small fish no longer have small fish to eat, and therefore, we affect the whole chain”, explains the professor. .

In corn and soybean crops, neonicotinoids are applied directly to the seed before it is planted. They have been used here since 2008.

In Quebec, it was estimated that in 2015, seeds coated with neonicotinoids were used on almost 100% of the corn crop acreage and on more than 50% of the soybean crop acreage.

Since they are no longer offered over the counter, their use has dropped remarkably.

According to the Quebec Pesticide Sales Report, in 2019, less than 2% of corn acreage and less than 1% of soybean acreage was sown with seeds coated with neonicotinoids. In 2020, it was only 0.2% of corn planted.

Impossible to speak to the MELCC expert

If they are now so little used, how is it that HVAC are so often outdated?

We requested an interview with the author of the report, Isabelle Giroux, on September 21st. The MELCC refused to make it available.

“The improvement is not always instantaneous, it can take a few months to a few years, because product residues can still be present in the soil following repeated use year after year and released into the waterways. during rain or snowmelt. The water quality criterion for the protection of aquatic species being very low, overruns can still be observed even a few years after an end to application”, however wrote the Ministry in a declaration that it sent to us. .

Agronomist Mathieu Leduc, who is a lecturer at the McDonald campus of McGill University, indicates that several factors can slow the degradation of pesticides. He points out that the years covered by the report were particularly dry. “There is probably the effect that by leaching less, it cleans the soil less quickly,” he points out.

He adds that in the case of pesticides buried in the ground, sunlight contributes less to the degradation of the chemical unlike products applied by watering.

” [Combien de temps] it’s going to take for the system to flush, it’s hard to say, he said.

“The conclusion is that maybe in environmental issues, we have to hurry to act now because it takes a long time before the ecosystem, the environment, recovers, cleans up and becomes natural again. . So that means that if we have a concern next year for another product, we should act quickly because if we wait 20 years, there will perhaps be 10 more years after that to wait until it’s really clean. »

Overview of the four witness rivers

Saint-Regis River (Montérégie)

43

• From 2018 to 2020, 30 to 43 pesticides or pesticide degradation products were detected in the Saint-Régis River.
• The chronic aquatic life criterion (CVAC) was exceeded for at least one pesticide in 100% of the samples in 2018 and 2019. The neonicotinoids thiamethoxam and imidacloprid are responsible for the majority of these exceedances.

Rivière des Hurons (Montérégie)

93%

• Overall, CVACs were exceeded in 93% of samples in 2018 and 2019, and in 60% of samples in 2020. The neonicotinoid insecticides clotianidin, imidacloprid and thiamethoxam are responsible for these exceedances, as well as the insecticide chlorantraniliprole to a lesser extent. measure.

Chibouet River (Montérégie)

96.7%

• The CVAC was exceeded for at least one pesticide in 96.7% of the samples collected in 2020.
• From 2018 to 2020, some 20 to 30 pesticides or degradation products have been detected in the river, depending on the year.

Saint-Zéphirin River (Centre-du-Quebec)

54.4%

• Although HVAC overruns are still “relatively frequent” in 2018-20, the report notes a “significant improvement” compared to the previous period. Overall, the frequency of CVAC exceedances for at least one pesticide decreased from 100% of samples for the 2015-2017 period to 54.4% for the 2018-2020 period.

A new insecticide causes concern

Three of the rivers in the report are located in Montérégie – the Chibouet River, the Des Hurons River and the Saint-Régis River – and one is in the Centre-du-Québec region – the Saint-Zéphirin.

Approximately 30 samples per season were taken at each station. From 2018 to 2020, between 19 and 43 pesticides or pesticide degradation products were detected in these rivers.

Among the batch is chlorantraniliprole, an insecticide that has replaced neonicotinoids in seed coatings and does not require agronomic justification.

Chlorantraniliprole is now detected in 99% to 100% of samples and concentrations are increasing in all four rivers. CVAC exceedances are “infrequent”, but have been observed in three of the four rivers, in particular in the Saint-Régis, where the frequency of exceedances reached 13% in 2020.

Set at 0.1 micrograms per liter (ug/l), the CVAC for chlorantraniliprole is “provisional,” the MELCC said in an email.

“The most obvious thing is that we are in the process of repeating the experiment with chlorantraniliprole. We don’t have a lot of information on its toxicity, and here we are testing across Quebec, ”underlines Sébastien Sauvé.