Less than two months after tourist crowds dispersed during COVID-19 restrictions, the world-famous Lagoon of Venice, Italy, experienced a 40% decrease in the number of identifiable pollutants known as volatile organic compounds, which are primarily derived from plastics, water traffic and tourism activity.

The Italian chemist who conducted the research, published April 7 in Science of the Total Environment, said the drastic drop in pollutants highlights the environmental toll of Venice's millions of annual visitors and the need to reduce plastic waste and other forms of pollution.

Her study is the first to investigate the connection between chemical pollutants and plastic waste in the sea, as well as how the presence of volatile organic compounds in Venetian water is tied to human activities.

"The lockdown provided a unique opportunity for comparing what was the quality of the water in Venice before the lockdown and after the lockdown," said Teresa Cecchi, a chemistry instructor at ITT Montani and the sole author of the study. "It's a magic side effect of this lockdown, from the scientific point of view."

Located in Northern Italy, Venice is a collection of small islands in a large lagoon that is famous for the canals running through the city. Although only about 53,000 people live in the historic city, tens of millions of people have visited the tourist destination annually for many years. But a lockdown implemented on March 10, 2020, to slow Italy's severe COVID-19 pandemic completely stopped tourism and severely reduced water traffic.

Videos of Venice's waters being cleared up during the lockdown went viral as an example of a positive environmental side effect of the pandemic. The increased visibility, however, was determined to be primarily because of reduced turbulence normally created by boats and cruise ships that kick up material from the bottom of the canals, and it was not necessarily a sign of less-polluted waters.

Cecchi investigated the water's pollution by conducting chemical analyses of water samples taken before and after Venice's lockdown, on Aug. 19, 2019 and May 3, 2020. She searched for volatile organic compounds, or VOCs, which easily dissolve in water and sometimes behave as water contaminants. They are used in the manufacturing of numerous products and include some alcohols, fuels, cleaning agents and chloroform.

From her 2019 water sample, Cecchi detected 132 such compounds and identified 40 of them. Although she did not hunt down the specific source of those with known identities, she determined that they were associated with numerous possible sources and uses. The mostly highly represented category was fragrances and flavoring agents, with 30 associated compounds, while 25 were used in fuels and 24 in plastic, rubber and epoxy resins.

Cigarettes, pharmaceuticals, disinfectants and motor maintenance were some of the other many categories associated with the volatile organic compounds. Collectively, the pollutants are tied to plastic waste, water traffic and the presence of tourists, as well as plants and microorganisms, Cecchi concluded.

"There are markers of cigarettes' butts and markers of fragrances and sunscreens and whatever we use every day in our everyday life," Cecchi said.

In the water collected in 2020, only 84 volatile organic compounds were detected and 24 were identified; this 40% drop was driven by 17 known compounds becoming undetectable, while one new compound appeared. The amounts of all but nine of the identified compounds fell after the lockdown, according to Cecchi, who said the stable compounds were probably more persistent or are still being deposited in the environment despite Venice's reduced activity.

"Obviously, overtourism is a problem because the environment is not able to process the molecules, which are released so abundantly in water," Cecchi said. "But the self-healing capacity we've shown is really rewarding, in my opinion."

The findings stress Venice's shortcomings in managing overtourism and waste and how they impact the surrounding waters, according to Davide Poletto, a project officer at the Venice bureau of UNESCO. Venice and its lagoon are a UNESCO World Heritage Site, which means they are designated for conservation for their cultural importance.

"Everybody [wants] to come here, but it's not easy to manage like a normal city — the waste collection, sorting the waste," Poletto said. Especially given the city's narrow streets and channels, it is "very easy for your cup, or whatever kind of waste, to be in one second on the ground, and the next one in the water."

Poletto provided water samples for the experiment during the lockdown, and he has been involved in other research on pollution in Venice. He was an author of a November report finding that plastics constituted the vast majority of floating litter in the water around Venice before the pandemic, with cigarette butts and packaging representing one-third of the surveyed plastics.

In addition to the need for putting less waste into the waters, the existing waste should be removed, Poletto said. He helped secure investment in efforts such as the European Union-funded In-No-Plastic to collect plastic waste from the Lagoon of Venice, where he said it often settles on the seafloor. 

Because recovered plastics are dirty and deteriorated, Poletto said the solution must be connected to chemical recycling, an uncommon method that decomposes the chemical structure of plastic for reuse rather than physically sorting and shredding the materials, as is done in standard mechanical recycling.

The study, "Analysis of volatiles organic compounds in Venice lagoon water reveals COVID 19 lockdown impact on microplastics and mass tourism related pollutants," published April 7 in Science of the Total Environment, was authored by Teresa Cecchi, ITT Montani.