Microplastics and Nonylphenol Act Together in Carp, but Mostly Without Synergy

Juvenile common carp exposed to polyethylene microplastics and the chemical 4-nonylphenol show widespread biochemical and cellular damage, but the two contaminants act largely in an additive fashion rather than synergistically, according to a new factorial laboratory study published in Ecotoxicology. The finding is notable because there has been inadequate knowledge of whether the joint action of these two contaminants departs from additivity, and this work shows that the answer depends on which biological endpoint is examined.

Researchers Esraa A. Anwari, Sally M. Salaah and Alaa El-Din H. Sayed assigned juvenile carp (Cyprinus carpio) to a fully crossed 2 × 2 factorial design: a control group, a group receiving 10 mg/L polyethylene microplastics (PE-MPs), a group receiving 200 µg/L 4-nonylphenol (4-NP), and a group exposed to the binary mixture. The exposure lasted two weeks and was followed by a two-week depuration period, allowing the team to track both the damage and any recovery.

The fish were assessed with a multi-biomarker approach spanning several biological levels. Antioxidant enzymes — superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) — were measured as indicators of oxidative stress. Neurological markers included acetylcholinesterase (AChE), monoamine oxidase (MAO) and nitric oxide (NO). The researchers also quantified the pro-inflammatory cytokines IL-1β and IL-6, DNA strand breakage, and apoptosis in red blood cells.

Both contaminants, alone and combined, significantly suppressed antioxidant enzyme activity and the neurological markers, while elevating cytokine levels, DNA strand breakage and erythrocyte apoptosis (all P < 0.05). Because the design was factorial, the team could formally test whether the mixture behaved differently from what the single-contaminant effects would predict, quantifying departures against both effect-addition and independent-action null models.

The interaction term was statistically significant at nine of the ten endpoints, but its direction depended on the biological process involved. Suppression of CAT, SOD and GPx, and the induction of apoptosis, were greater than additive — a synergistic pattern. In contrast, inhibition of AChE, MAO and NO, and elevation of IL-1β and IL-6, were less than additive, indicating antagonism. DNA strand breakage showed no significant interaction at all.

Crucially, however, none of these departures from additivity exceeded the two-fold threshold conventionally required to call a mixture toxicologically synergistic. The authors therefore describe the joint action as approximately additive, with endpoint-specific modulation, rather than broadly synergistic — a more cautious conclusion than dramatic accounts of microplastic-chemical mixtures often imply.

The depuration phase revealed that some effects linger far longer than others. Two weeks in clean water abolished the antagonistic interactions at the cholinergic and monoaminergic endpoints and returned DNA strand breakage in the single-contaminant groups to control values. But antioxidant enzyme activity did not recover, cytokine elevation persisted, and apoptosis in the mixture group remained more than five-fold above control levels.

Serum protein electrophoretic profiles differed in fraction number and molecular weight distribution across the treated groups, though the authors note these profiles derive from a single pooled sample per group and are reported descriptively rather than statistically.

A three-way analysis added a further layer of nuance: the interaction itself changed significantly between the exposure and depuration phases at six of the ten endpoints. In other words, whether the mixture behaves synergistically or antagonistically at a given biomarker is a time-dependent property, not a fixed characteristic of the contaminant pair.

The authors conclude that hazard assessments relying on a single biomarker or a single time point may misrepresent the joint risk of microplastic-associated contaminants in aquatic ecosystems. For juvenile carp in this laboratory setting, the mixture’s most persistent damage appeared in oxidative stress, inflammation and cell death, long after the more transient neurological effects had faded.

Subject of Research: Combined toxicity of polyethylene microplastics and 4-nonylphenol in juvenile common carp assessed with a multi-biomarker factorial design

Article Title: Combined toxic effects of polyethylene microplastics (PE-MPs) and 4-nonylphenol on the common carp (Cyprinus carpio) juvenile: multi-biomarker approach

Article References: Anwari, E. A., Salaah, S. M., & Sayed, A. E.-D. H. (2026). Combined toxic effects of polyethylene microplastics (PE-MPs) and 4-nonylphenol on the common carp (Cyprinus carpio) juvenile: multi-biomarker approach. Ecotoxicology, 35(9), Article 192. https://doi.org/10.1007/s10646-026-03167-9

Image Credits: AI Generated

DOI: 10.1007/s10646-026-03167-9

Keywords: polyethylene microplastics, 4-nonylphenol, common carp, mixture toxicity, oxidative stress, biomarkers, apoptosis, cytokines, depuration, ecotoxicology, factorial design, aquatic toxicology