Early Life Stage Bioactivity Assessment of Short-Chain Chlorinated Paraffins at Environmentally Relevant Concentrations by Concentration-Dependent Transcriptomic Analysis of Zebrafish Embryos

Short-chain chlorinated paraffins (SCCPs),
a class of ubiquitous pollutants, are considered to be embryotoxic
and teratogenic. However, little is known regarding the bioactivity
and mechanisms at environmentally relevant concentrations at the embryonic
period. Here, a concentration-dependent reduced transcriptomic approach
was used to evaluate the environmental dose (<100 ppb) effects
of nine SCCP congeners and eight commercial mixtures on zebrafish
embryos at 8 hpf. After 24 h of exposure, the overall biological potency
of all the SCCPs, in terms of interference with 20% of the differentially
expressed genes (PODDEG20), in zebrafish embryos ranged
from 0.83 to 67.61 ppb. C10H14Cl8 (PODGO20 = 3.80 ppb) and C10–13 51.5%
Cl (PODGO20 = 3.31 ppb) exhibited the strongest interference
with biological processes compared to other SCCP homologs and mixtures,
respectively. The most sensitive early molecular responses induced
by SCCPs were associated with pathways of genetic damage, energy metabolite
interference, and metal ion binding. Furthermore, the carbon number
was positively correlated with the transcriptomic potency (PODGO20) of SCCP congeners (with chlorine content > 60%) (p = 0.038), and the chlorine content of SCCP congeners affected
the bioactivity associated with genotoxic pathways. The concentration-dependent
reduced transcriptomic approach significantly improved the understanding
of the ecological risk of environmental contaminants at early life
stages.