By Jana del Favero and Fernanda I. Colabuono
Illustration by Joana Dias Ho
Pesticides are substances, mixtures of substances, or even biological agents (such as viruses and bacteria) that can prevent, combat, or exterminate species that cause damage during the production, harvest, and storage of food, or that cause harm to public health (e.g. insect vectors of disease). They are important in agriculture because, by controlling pests, they promote an increase in crop production and/or quality. However, their indiscriminate use causes several environmental and human health problems, since they can also be toxic to non-target species. Non-target species include a multitude of animals, including you, me, and the seabirds that we will focus on in this post. Many pesticides are named according to the type of pest they attack, for example: insecticides are used for insect control, herbicides for weed control, fungicides for fungus, among several other names. “Agrochemical”, a term which we commonly hear, is the legal term for pesticides and is defined in the Brazilian Law 7802/89, also called the Agrochemicals Law. They can be classified as agricultural or non-agricultural (learn more about them here).
The transport of agrochemicals from soil into bodies of water occurs mainly due to surface runoff generated by rainfall or crop irrigation. Rivers act as an expressway for agrochemicals, quickly transporting them to lakes and the ocean. As many agrochemicals are highly stable chemical compounds (i.e. difficult to degrade or be metabolized), they persist in the environment for a long time. Thus, they can be transported over long distances and even occur in regions where they have never been used, such as in Antarctica!
Once in the oceans, pesticides are absorbed by plankton (reminder about them here) and are transported, via food, to higher trophic levels in a process called biomagnification. An example of biomagnification is shown in the figure below, where you can see how the concentration of a substance in ppm (parts per million) increases at each trophic level: producers < zooplankton < small fish < large fish < fish-eating birds. It is important to remember that many fish and birds have migratory habits, serving as a means of transporting pesticides to other regions.
Example of biomagnification in a trophic chain (image by © cmassengale)
One of the first and most famous pesticides, DDT (an acronym for Dichloro Diphenyl Trichloroethane, that coined the verb “to dedetize”), was widely used during and after World War II to combat mosquitoes that carry malaria and typhus, because it was cheap and highly effective in the short term. However, in the long term it had harmful effects on the environment, as cautioned by the American biologist Rachel Carson in her book "Silent Spring." Carson claimed that DDT caused the thinning of eggshells, resulting in reproductive problems and the death of birds. The book "Silent Spring" helped ban DDT in the United States in the 1970s, followed by several other countries (it was only in 2009 that the ban made its way to Brazil!).
Although DDT was banned in most countries decades ago and has never been used in Antarctica, in her post-doctoral work, Fernanda analyzed the eggs of some Antarctic bird species, such as penguins, petrels and skuas, and found the presence of DDT and other pesticides in them, illustrating how these substances persist in the environment and reach even remote areas. But don't think that the transfer through the food web (as shown in the biomagnification figure) is the only way pesticides reach birds. Humans have added another food item to the seabirds' menu: PLASTICS! Seabirds accidentally mistake plastic items for a food and ingest them, potentially irreversibly damaging the individual (e.g. obstruction of the digestive tract, decreased appetite, etc.).
Furthermore, plastics absorb pesticides (i.e. the molecules of the substance in question adhere to the surface of the plastic). In addition to all the harm caused by ingesting the plastic alone, the birds are exposed to the pesticides and other pollutants coating them! In a paper published in 2010, Fernanda and her collaborators evaluated the plastic objects ingested by birds sampled in southern Brazil, and found pesticides on them.
Albatross chick found dead with plastics in its stomach (Photo by Chris Jordan, public use)
Unfortunately, the concentration of pesticides is increasing year by year, and they are found in the soil, in the atmosphere, in the water, and in living animals. Brazil is one of the largest consumers of agrochemicals in the world, with indiscriminate use of pesticides in many cases. This picture needs to change. Seabirds and the health of your own body will thank you!
For more information:
Colabuono, F.I., et al. (2010) Polychlorinated biphenyl and organochlorine pesticides in plastics ingested by seabirds. Marine Pollution Bulletin 60, 630-634. Disponível em: http://www.sciencedirect.com/science/article/pii/S0025326X10000366
Colabuono, F.I., et al. (2015). Organochlorine contaminants and polybrominated diphenyl ethers in eggs and embryos of Antarctic birds. Antarctic Science 27(4), 355–361. doi:10.1017/S0954102014000807
Colabuono, F.I., et al. (2016). Persistent organic pollutants in blood samples of Southern Giant Petrels (Macronectes giganteus) from the South Shetland Islands, Antarctica. Environmental Pollution 216, 38-45. Disponível em: http://www.sciencedirect.com/science/article/pii/S0269749116304298.
Dossiê ABRASCO: um alerta sobre os impactos dos agrotóxicos na saúde / Organização de Fernando Ferreira Carneiro, Lia Giraldo da Silva Augusto, Raquel Maria Rigotto, Karen Friedrich e André Campos Búrigo. - Rio de Janeiro: EPSJV; São Paulo: Expressão Popular, 2015. 624 p. Disponível em: http://www.abrasco.org.br/dossieagrotoxicos/wp-content/uploads/2013/10/DossieAbrasco_2015_web.pdf
Fernanda Colabuono has published another post here.