Mullin and English partner Zara Dampney were promoted to the main draw for the event but lost both of their matches.
Experienced Georgian pair Christine Santanna and Andrezza Martins defeated them 21-13, 21-18 and then the British duo went down to Puerto Ricans Dariam Acevedo and Yarleen Santiago 18-21, 6-21. It meant the pair finished 25th.
Mullin and Dampney, who had a top-ten finish in Kristiansand, Norway, last summer are looking to enhance their reputation on the world circuit this year.
The pair, who train full time in Bath, are seeking to crank up a gear ahead of the 2012 Olympics in London. In the men's tournament in Brasilia, Edinburgh's Robin Medzybrodzki and English partner Gregg Weaver went down 21-13, 13-21, 14-16 to Australians Chris McHugh and Josh Slack in the qualifying and finished 41st overall.
This weekend sees the climax of the Scottish indoor season with the finals of the national cups but the main silverware is heading west.
Glasgow Ragazzi, who knocked out City of Edinburgh in the semi-finals, face Glasgow Mets in the men's Scottish Cup final and Troon PA face Su Ragazz in the women's final.
But there is still Edinburgh interest with Grassmarket Jets taking on Su Ragazzi II in the final of the men's Plate and City of Edinburgh II taking on Troon KC in the women's Plate. City of Edinburgh face South Ayrshire in the women's Thistle Bowl and the same clubs meet in the men's junior national league final.