Forbidden, but not gone: Past sins and today's pesticides appear in bird eggs

Bird eggs can reveal our pollution of nature. They show that our use of pesticides affects more than just pests and weeds in the fields, and especially that the use of now banned pesticides from earlier times is still present in our ecosystems. A new study demonstrates this, where researchers over a decade collected and examined 89 unhatched/miscarried eggs and eggshells from 14 different bird species in Spain. "By using eggs as a tool for biomonitoring, we get an overview that allows us to determine which pollutants are circulating in the ecosystems," says Nahúm Ayala, a researcher in veterinary toxicology and the lead of the study, in a press release. The eggs were analyzed for heavy metals, 293 pharmaceuticals, 274 pesticides, and 11 PCBs, which among other things, have been used as plastic softeners before being banned in the EU in the 1980s. The levels of heavy metals were generally very low, and the researchers found no traces of medicine in their samples — although they mention that in two eggs included in this study's other analyses, traces of painkillers had previously been found in a separate study from the same laboratory. Banned for several decades. The story was different for pesticides and PCBs: analyses showed, among other things, that samples from three bird species contained PCBs, and in samples from eight species, they found breakdown products of the insecticide DDT, which was banned in Spain in the 1970s due to its harmful effects on our health and ecosystems. Since then, it has been banned for agricultural use in most of the world. "These types of pollutants directly affect reproduction in species like the griffon vulture, which only lay one or two eggs a year, making reproductive failure a significant problem. The presence of DDT, for example, is associated with thinning eggshells, making them more susceptible to microbial invasion and moisture loss, thus endangering the eggs," explains Isabel Fernández, a researcher at CAD and the main author of the study, in a press release. However, they did not see signs that DDT had thinned the eggshells in these cases. Several fungicides, herbicides, and insecticides, which are now either approved in the EU, being phased out, or illegal, were also found in the eggs. A chemical used on citrus fruits. In some cases, fungicides such as imazalil — used as a surface treatment on citrus fruits, which are also imported to Denmark — prochloraz, and tebuconazole were found in what the researchers call "high concentrations." Prochloraz is illegal to use in the EU, while tebuconazole, a systemic fungicide, is still permitted. Previous research has shown that exposure to tebuconazole in certain bird species can be endocrine-disrupting for the mother bird and affect fetal development. The researchers also found several eggs that were not contaminated, which they interpret as an indication that it is possible to eliminate pollution. They also note that their egg analyses cannot be used to conclude that the presence of chemicals was the cause of the eggs not hatching, and that these are samples, so no general conclusion about pollution can be drawn. The study was published in the journal Ecotoxicology and Environmental Safety.