What substance is being sprayed during this scene in Chernobyl?

In HBO’s Chernobyl series, after reactor no. 4’s meltdown, soldiers (Chernobyl’s liquidators) splash a light-brown liquid onto the ground, both streets and forest, and for washing vehicles; for this operation they used a variety of means (manned pumps, trucks, helicopters).

Here are some screenshots:

What is the reason they do this?
What substance are they spraying?

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@CGCampbell (from the Movies & TV stack…) pointed out this page, where photos described as:

Liquidators wash the radioactive dust off the streets using a product called “bourda”, meaning molasses" and "Helicopters spray the area with dust suppressant.