so all goods and services that require said "dirty job" in the supply chain will go up in price. This eventually negates the UBI benefits, because the level of UBI no longer can sustain purchases of all the goods and services that it originally could due to the increases in prices.
So do you increase UBI to counter this? Or do you let it be, and UBI no longer pays enough to maintain the same level of living standard. In which case, people are now once again, forced economically, to work "dirty jobs" despite not wanting it.