After soaking lemons and limes in water overnight, they have white spots all over them - what is that?

I'm trying to make limoncello. I wasn't able to find organic lemons and limes so I bought regular ones and planned to clean them very well since limoncello uses the rind which can have pesticides and waxes on it. So I soaked them overnight and tried to scrub them with a brush, but now they have these white spots. Is that a fungus? I'm worried to use the zest.