Fulvic acids (FA)
Fulvic acids can be formed in water, or they are low molecular weight end members of humic acids from soil leaching.
They have even fewer (highly substituted) rings than HSperhaps even only conjugated systems resulting from ring cleavage.
They contain a high proportion of acid functional groups, whereby the subdivision into core and shell regions is blurred. The molar masses are between 600 - 1,000 g/mol.
FAs are highly soluble in both alkaline and acidic solutions.