By Anthony Boadle
BRASILIA (Reuters) - Brazilian President Dilma Rousseff's popularity slumped to a new low and support for her impeachment grew amid a deepening corruption scandal and a severe economic downturn, according to an opinion poll published on Tuesday.
The numbers are another blow for Rousseff, who is facing criticism from within her own leftist Workers' Party over fiscal austerity measures she has adopted to try to save Brazil's prized investment grade.
The CNT/MDA poll showed that her government's approval rating has fallen to 7.7 percent compared with 10.8 percent in a previous survey in March, while 70.9 percent rate her government negatively compared to 64.8 percent in March.
The number of respondents who favour Rousseff's impeachment over a massive kickback scandal at state-run oil company Petroleo Brasileiro SA (SA:PETR4) has risen to 62.8 percent from 59.7 percent four months ago.
Preferred shares of Petrobras rose about 3 percent in early Tuesday trading after the poll came out. Many investors believe Rousseff's impeachment would lead to better management of the company.
Brazilians favouring impeachment want Rousseff ousted for corruption at Petrobras, which she chaired before becoming president in 2011. Many who favour her impeachment also cite alleged campaign finance irregularities and government accounting mismanagement during her first term, the poll said.
The survey showed that a vast majority of Brazilians - 84.6 percent - believe Rousseff is unable to handle the country's worst economic downturn in 25 years, with gross domestic product is expected to shrink 1.7 percent this year.
More than 50 politicians, mostly from Rousseff's governing coalition, are under investigation for kickbacks received from Brazil's top engineering and construction firms skimmed from overpriced contracts with Petrobras.
Rousseff is not being investigated but her opponents have stepped up demands for her impeachment, which would require proof that kickback money funded her election campaign. Rousseff and the Workers' Party say all campaign donations were legal.
The political risk consultancy Eurasia earlier this month raised to 30 percent from 20 percent the chances a Rousseff impeachment, which would require an unlikely alignment between her main ally the PMDB party and the main opposition party PSDB.
The MDA poll, commissioned by the national transport lobby group CNT, surveyed 2,002 people between July 12 and 16. The margin of error was 2.2 percentage points.