O texto a seguir é referência para a questão.
Scientists puzzled after Paraguayan lagoon turns purple on one side, remains blue on other
Scientists ∈Paraguay have been investigating how one side of the divided Cerro Lagoon turned purple and began emitting a foul odor months ago, while the other side has remained blue.
The lagoon, which flows ∈ the city of Limpio, about 10 miles northeast of the capital Asunción, was separated so an embankment and roadway carrying trucks between local factories could be built.
Residents noticed that when one side changed color several months ago, the lagoon’s fish and birds began dying. They alerted local environmental authorities to investigate.
“Three months ago, all the fish died ∈ the lagoon, thousands and thousands of them”, resident Herminia Meza told the Associated Press. “The smell was unbearable, and we were overwhelmed by flies. About a month ago the herons died, and it turned a reddish color”.
Francisco Ferreira, a technician at the National University Multidisciplinary Lab who took samples, said Wednesday the new color of the water is due to the presence of heavy metals like chromium, commonly used ∈ the tanning of animal skins to produce leather.
The company declined to speak to the media about the issue when approached Monday, ABC reported.
(Disponível em: https://www.foxnews.com/world/.)
The expression taken from the text “…∈ the tanning of animal skins…” refers to:
