Corruption has emerged as a major concern for Brazilian voters ahead of the October 25 presidential runoff between far-right candidate Flávio Bolsonaro and leftist Luiz Inácio Lula da Silva. However, experts say its biggest impact may be on voter turnout rather than on voters' choice between the two candidates.

Both candidates are associated with corruption allegations in the eyes of many Brazilians. Bolsonaro is under investigation for corruption, money laundering and tax evasion, while Lula spent 19 months in prison on corruption and money laundering charges that were later annulled.

For staunch supporters of either candidate, such allegations are unlikely to weaken their loyalty. However, experts say widespread perceptions of corruption could discourage people from voting and fuel anti-incumbency sentiment, potentially benefiting Bolsonaro, who received 2.2 million more votes than Lula in the first round.

Brazil remains deeply polarised

During the first round, many voters wore red hats and T-shirts to show support for Lula's party, while others donned the yellow and green colours of the Brazilian flag adopted by Bolsonaro's movement, reflecting the country's deep political divisions.

Supporters of both candidates are highly distrustful of the opposing camp and view it as a threat. Experts say such voters are less likely to be swayed by corruption allegations against their preferred candidates.

"We have a great ability to filter information that goes against our beliefs," said Nara Pavão, a political science professor at the Federal University of Pernambuco. "People don't want to discover the truth about their candidates, they want to beat the opponent."

Camila Tobji de Aquino, a 19-year-old student of pedagogy and psychology, said corruption was a problem across political parties in Brazil. However, her main concern was what she viewed as the threat Flávio Bolsonaro posed to democracy.

"If I were to vote only for a candidate not tied to any corruption, I would vote blank," she said. "But that's not the choice Brazil is facing. For me it's a question of being able to vote in the next election."

Corruption scandals contribute to rising abstention

A wide-ranging scandal involving politicians and Supreme Court judges has dominated headlines ahead of the election, placing corruption at the centre of public debate.

Justice Alexandre de Moraes, who presided over the legal case that led to former President Jair Bolsonaro's imprisonment over his attempted coup, is suspected of having links to the former head of the failed Banco Master bank. Flávio Bolsonaro has also faced allegations of links to the bank. Both have denied wrongdoing.

For many Brazilians, the Banco Master controversy has revived memories of Operation Car Wash, the country's largest corruption and money-laundering investigation, launched in 2014 and involving dozens of politicians.

Repeated corruption scandals could increase abstention and influence undecided voters, said Laura Chelidonopoulos, a political science PhD candidate at the University of Pittsburgh who has studied corruption.

"People become disenchanted with politics," she said. "They have less motivation to actually choose between one of these two sides."

More than 33 million people, or 21% of eligible voters, did not cast ballots on October 4, marking the highest abstention rate in a first round since 1998. Data from Brazil's electoral court show that first-round abstention has gradually increased since 2006.

Voters call for change

José Tainan, a 36-year-old kitchen assistant from Rio de Janeiro's Penha favela complex, said he could hardly remember the last time he voted, though he believed it was probably for Lula sometime in the 2000s.

He cited corruption as the main reason for abandoning voting.

"There are no good options. Neither one of them suits me. I would rather justify why I didn't vote," he said.

Voting is compulsory in Brazil for citizens aged 18 to 70. Those who fail to vote without a valid reason face a small fine.

Matusalem Aguiar, a 54-year-old taxi driver from Belford Roxo, an impoverished municipality near Rio de Janeiro, said he would prefer that only candidates with clean records be allowed to run for office. Despite that view, he plans to vote for Bolsonaro, disregarding the corruption investigations involving the candidate.

"There needs to be a change," Aguiar said while waiting for his next passenger in downtown Rio. "Some people have a lot of power and they're not managing the country in the right way."