The pesticide DDT persists in remote lakes at concerning levels half a century it was banned, affecting critical marine species and potentially entire lake food webs, according to new findings of a multi-university research team published in the peer-reviewed journal Environmental Science & Technology of the American Chemical Society, the world's largest scientific society.
The lead author of the study and an Assistant Professor in Geology and Environment at Mount Allison University, Dr. Josh Kurek, said that what was considered environmental crisis yesterday in the 1950s through 1970s remains today's problem. Decades of intensive insecticide applications to our conifer forests have left a lasting mark on these lakes, and likely many others in eastern North America.
Before legal restriction between 1950 and 1970, dichlorodiphenyltrichloroethane (DDT) insecticides were widely applied to eastern North American forests to manage naturally occurring insect outbreaks including spruce budworm. Although often implemented to forests by airplane, chemicals like DDT are highly persistent and can eventually wash into lakes from their surrounding landscape.
The new research examined dated sediments from the bottom of five remote lakes located within different watersheds in north-central New Brunswick, Canada. Lake sediments provide a well-recognized and authoritative archive of environmental conditions which allows researchers to assess chemical and biological conditions in lakes before, during, and after the use of pesticide. The study highlights the chemical legacy of one of North America's most extensive aerial spray programs of insecticides ever coordinated by forest stakeholders.
Historical trends in the lake sediments mirrored the known use of this pesticide in the province, with high levels of DDT in sediment layers from the 1960s and 70s. Levels of DDT in lake sediments were among the highest found in previously-sprayed areas of Canada and the U.S., suggesting very intensive past use of pesticides for spruce budworm control. Surprisingly, DDT and its toxic breakdown products are still quite high in modern sediments, above levels where harmful biological effects tend to occur.
Also, an essential invertebrate within lake food webs, the small water flea Daphnia sp. has declined substantially, often coincident with increased DDT. Loss of Daphnia sp. often negatively impacts lake food webs. These impacts may lead to higher algae production and fewer preys for fish.
The co-author of the study, a professor at McMaster University, and Chair in Environment and Health, Sr. Karen Kidd, said that they had learned a lot of tough lessons from the heavy use of DDT in agriculture and forestry. The biggest one is that this pesticide was concentrated through food webs to levels that caused widespread raptor declines in North America. Dr. Kidd added that the lesson from their study is that pesticide use can result in persistent and permanent changes in aquatic ecosystems.
