# Perfluoroalkyl and Polyfluoroalkyl Substances Release from Biosolid-Derived Compost

## TL;DR

This study examines how PFAS chemicals are released from compost made from biosolids, showing that release patterns depend on chemical structure and solution conditions.

## Contribution

The study introduces a novel method using sequential leaching to analyze PFAS release mechanisms from compost.

## Key findings

- PFAS desorption followed a biphasic pattern, with rapid initial release and a slower sustained phase.
- Electrostatic interactions and DOM complexation significantly influenced PFAS mobility.
- Short-chain PFAS like PFHxA and PFHxS released quickly, while longer-chain PFAS showed prolonged desorption.

## Abstract

This study investigated the release potential and controlling
mechanisms
of representative per- and polyfluoroalkyl substances (PFAS) of varying
carbon-chain lengths from a commercial biosolid-derived compost using
sequential leaching with water and saline solutions (10 mM NaCl and
5 mM CaCl2). The compost contained >40% organic matter,
PFAS concentrations up to 140 ng·g–1, and precursor
levels below 5 ng·g–1. Eluate analyses revealed
dissolved organic matter (DOM) concentrations up to 1400 mg·L–1 and major ions (Ca, Mg, Na, K, Cl, P, and S) reaching
600 mg·L–1, accompanied by PFAS concentrations
up to 2600 ng·L–1. PFAS desorption followed
a biphasic patternrapid release within the first hour followed
by a slower, sustained phase over 48 hwell described by a
first-order two-compartment model with rate constants k
1 = 1–7 h–1 and k
2 = 0.001–0.016 h–1. Electrostatic
interactions dominated the desorption process, as both Na+ and Ca2+ reduced the fraction of fast-release sites (F
1), with Ca2+ showing a stronger
suppression due to cation bridging and charge screening. Perfluorohexanoic
acid (PFHxA) and perfluorohexanesulfonic acid (PFHxS) were almost
completely released within 1 h, whereas perfluorobutanoic acid (PFBA),
perfluorobutanesulfonic acid (PFBS), perfluorooctanoic acid (PFOA),
and perfluorooctanesulfonate (PFOS) exhibited prolonged desorption
associated with interactions with solid organic matter and DOM. DOM-facilitated
desorption was evident, as PFAS–DOM complexation enhanced release
under certain ionic conditions. Overall, the results reveal the intricate
coupling among compost matrix properties, PFAS molecular structure,
and eluent chemistry governing PFAS mobility.