In recent years, many storks that traditionally migrate to Africa in the cold months stay to spend the winter in the Peninsula, where they have abundant food in the garbage dumps. However, it is precisely those that do migrate to the African continent that could be contaminating their organisms with pesticides, according to a team of Extremadura scientists who have analyzed the blood of chickens from three colonies, two of them installed near waste deposits . The main source of contamination seems to come from insecticides used even in African countries where some of the birds migrate and transfer their load to the young through their eggs.
In Europe, white storks ( Ciconia ciconia ) are losing their population, but in Spain these birds, which are mainly concentrated in Castilla-La Mancha and Extremadura, are still very numerous. Only in the province of Cáceres there are about 7,000 couples that increasingly emigrate to Africa less. As birds accumulate organic pollutants in their organisms, the Extremadura team decided to check the levels of contamination by persistent organic compounds (POPs), specifically organochlorine pesticides (OCP) and polychlorinated biphenyls (PCBs), in 59 chickens from three Extremadura colonies with different levels of environmental exposure with respect to urban solid waste treatment centers or controlled garbage dumps: in a protected area for birds (ZEPA Llanos de Cáceres and Sierra de Fuentes), another surrounded by pasture five kilometers from the dump; and the last in an agricultural area two kilometers from another garbage dump.
The results confirm the absence in the plasma of the chickens of PCBs, currently prohibited substances that had been detected in two previous investigations carried out with stork chickens in the province of Madrid, in a more industrial and populated area. However, traces of chlorinated insecticides such as heptachlor, endosulfan, aldrin and DDE (dichlorodiphenyl dichloroethylene, a metabolite of the well-known insecticide DDT) did appear which, although prohibited, remain in the environment for a long time and accumulate in the trophic chain. .
The most striking thing is that in chickens from the colony closest to the garbage dump, the levels of these pesticides were lower than in individuals from the other three colonies. The colony with the most presence and highest levels of chlorinated insecticides was the one surrounded by pasture. In the absence of a pattern linking the landfill to the pollutant load on birds, scientists believe the contamination may be due to the winter migration of mothers to Africa.
In developing countries, many of the pesticides banned in Spain are still widely used. For example, the insecticide DDT is used in agriculture and to control malaria-transmitting mosquitoes , and this could be the main source of these pollutants in storks, which when they return to the Peninsula, transfer part of their pollutant load chickens through the egg yolk, which has a high fat content.
OCPs can affect the reproductive properties of birds, and cause the feminization of males, the inhibition and reduction of the number of eggs in each laying, the alteration of behavior during rearing or deformities in the embryos. Storks are poisoned through plant foods and small animals such as rodents, worms and frogs, previously contaminated by these compounds, which can persist in the environment for several decades. For this reason, stork chicks, due to their size, easy location, control and sampling, are good indicators of environmental contamination.
