Legacy pesticides (µg/kg dry weight)
Legacy pesticides (µg/kg wet weight)
What are they?
Organochlorine pesticides (OCPs) are also known as ‘legacy’ pesticides. Their use was banned or restricted in the 1970s and 1980s in North America and many other countries, yet they persist in the environment today. Beginning in the 1940s, OCPs were widely used in agriculture and for general pest control. Nine of the 12 most hazardous persistent organic pollutants (POPs) targeted by the Stockholm Convention in 2001 for elimination on a global scale are OCPs: dichlorodiphenyltrichloroethane (DDT), dieldrin, aldrin, chlordane, mirex, endrin, heptachlor, hexachlorobenzene, and toxaphene. 1 However, not all countries are signatories to the Stockholm Convention, and use of OCPs continues in some parts of the world.
Which ones were detected?
Legacy pesticides detected during Phase 1 (2015 – 2017) and Phase 2 (2018 – 2020) are summarized in Table 1.
Table 1. Legacy pesticides detected during Phase 1 and Phase 2
How do they get into the ocean?
Historically, OCPs entered the marine environment through wastewater discharges and run-off from agricultural lands. Today, where OCPs are banned or heavily restricted, redistribution of OCPs that persist in soil and sediment, and global transport via atmospheric and oceanic currents are the main sources. OCPs are persistent, remaining in the environment for decades. They are also soluble in lipids, allowing them to accumulate in the fatty tissues of organisms.5
Are they a problem?
Organochlorine pesticides have a range of toxic effects in humans and other organisms, including damage to reproductive and neurological functions, ability to cause cancer, and hormone disruption.5
FACT: The endocrine-disrupting properties of DDT contributed to a classic case of ‘cause-and-effect’ in wildlife toxicology. Populations of fish-eating birds, including eagles, cormorants and pelicans declined in North America and Europe because of DDT-associated eggshell thinning.3
OCPs such as DDT and lindane are acutely toxic to a wide range of aquatic species. DDT is also highly toxic to bird embryos and can impair egg-shell quality. The reproductive success of bald eagles and other raptors was highly compromised in the 1950s and 1960s partly as a result of DDT exposure. Bald eagle populations began to recover in the 1970s following the ban on DDT in Canada and the United States.5
In salmon, agricultural OCPs have been shown to impair their sense of smell and disrupt their ability to return to their natal streams.5
What is being done?
Organochlorine pesticide use is largely banned in North America, greatly reducing new inputs to the environment. Since OCPs are no longer imported or used in Canada, clean-up of contaminated areas is key to prevent further marine pollution.
Canadian federal 7 and provincial 6 marine sediment quality guidelines protective of marine invertebrates are available for several OCPs (Table 1). However, tissue residue guidelines for the protection of wildlife consumers of aquatic biota are only available for DDT.
On a global scale, the Stockholm Convention aims to eliminate the use of the most toxic OCPs. Reductions in the global use of OCPs will help decrease inputs and adverse human and environmental effects in both source regions and other parts of the world.
What can you do?
Although the use of legacy OCPs is not permitted in Canada today these persistent compounds remain in the environment, and new pesticides have been developed to replace them. Individuals and organizations can:
- Learn more about organochlorine pesticides and their current-use alternatives using the resource links below
- Reduce or eliminate the use of chemical pesticides around the household and garden
- Recycle and dispose of waste according to local regulations
1 Stockholm Convention. 2017. All POPs listed in the Stockholm Convention. Available at: Listing of POPs in the Stockholm Convention
2 Health Canada. 2020. List of toxic substances managed under Canadian Environmental Protection Act. Available at: Toxic substances list – Canada.ca
3 Bergman Å, Heindel JJ, Jobling S, Kidd KA, Zoeller RT. 2012. State of the science of endocrine disrupting chemicals. Geneva: United Nations Environment Programme and World Health Organization. 289 pp. ISBN: 978 92 4 150503 1. Available at: https://apps.who.int/iris/bitstream/handle/10665/78101/9789241505031_eng.pdf
4 Agency for Toxic Substances and Disease Registry (ATSDR). 2017. Toxic Substances Portal. Available at: https://www.atsdr.cdc.gov/toxfaqs/index.asp
5 Garrett C and Ross PS. 2010. Recovering resident killer whales: a guide to contaminant sources, mitigation, and regulations in British Columbia. Canadian Technical Report of Fisheries and Aquatic Sciences 2894.
6 British Columbia Ministry of Environment and Climate Change Strategy. 2021. Working Water Quality Guidelines: Aquatic Life, Wildlife and Agriculture. Water Quality Guideline Series, WQG-08. Prov. B.C., Victoria B.C. Available at: https://www2.gov.bc.ca/assets/gov/environment/air-land-water/water/waterquality/water-quality-guidelines/bc_env_working_water_quality_guidelines.pdf
7 Canadian Council of Ministers of the Environment (CCME). 2022. Available at: Canadian Council of Ministers of the Environment | Le Conseil canadien des ministres de l’environment (ccme.ca)