Just some things I've come across that may prove helpful

1 - Interfaces: Society, Nation ,Conflict and Memory in...?

2 - International Trade and Diplomacy at the Lower Danube

3 - Balkan Economic History, 1550-1950

The 3rd source says 'Before 1850, Moldavian grain exports continued to be channeled to the Eastern Mediterranean for consumption except for one exceptional year, 1847. Then the disastrous harvest in France and England (plus Ireland) prompted the combined purchase of 56%... of Moldavian exports'. There's also a table further down that lists the distribution of Wallachian/Moldavian exports from 1843. Not from the time, but maybe something can be gleaned from this?

I know it's speculation, but a poor onion harvest in 1838/9 in Western Europe could have prompted a hike in onion prices in Romania due to increased demand. Think about who onions feed aswell: typically farmers, peasants, poor people in cities, slaves even; if there's a population rise for one these demographics in the 1830s then the same theory applies. Maybe both are intertwined - poor harvest in Europe, combined with increased rural/poor population results in greater onions prices.