Depends what you mean by “1–2% plastic,” because humans (and journalists) love using a precise number to describe a fuzzy nightmare.

1) If you mean “1–2% of body mass is plastic in the gut” (mostly macroplastic, sometimes mixed sizes)

Yes, we have real-world and necropsy-based evidence in wildlife, especially seabirds.

• Sub-lethal harm shows up around the ~1–3% body-mass load range (in birds). A 2025 study on shearwater fledglings discusses plastic loads and argues negative impacts tend to appear when ingested plastic reaches roughly 1–3% of body mass (based on their data plus global findings).

• “Plasticosis” (scarring/fibrosis of the stomach) is documented in wild seabirds and is strongly associated with plastic in the digestive tract, with measurable tissue structure damage and collagen/scar changes.

• Mortality risk rises sharply with relatively small plastic burdens in marine megafauna. A 2025 PNAS analysis using >10,000 necropsies modeled plastic-associated death risk; they report 90% mortality risk thresholds on the order of dozens of items for seabirds (and larger counts for bigger animals), with risk also depending on plastic type.

So, for animals that are “1–2% plastic” in the sense of gut load, the observed/estimated outcomes include: reduced body condition/growth, digestive tract injury and scarring, altered physiology, and in enough cases death (especially with certain plastic types).

2) If you mean “1–2% of the animal’s tissues are plastic”

That’s a totally different claim, and we basically do not have evidence that animals’ organs are literally 1–2% plastic by mass in the wild. Tissue measurements exist (micro/nanoplastics detected in organs), but turning that into “percent of body mass” at 1–2% would be… extraordinary, and would require extraordinary measurement controls.

3) If you mean “they’re eating microplastics at ~1–2% of their diet” (lab experiments)

Labs do run high-exposure experiments (sometimes framed as % w/w in feed or very high particle concentrations), and the common findings across species include:

• gut microbiome shifts, barrier dysfunction, inflammation, metabolic effects in mice under certain conditions (diet context matters a lot).

• reproduction/survival impacts in small aquatic organisms (Daphnia especially), often depending on food availability, particle shape/size, and exposure duration.

But those are dose-model studies, not “this many percent of the animal is plastic now.”

The clean takeaway (since reality refuses to be clean)

• 1–2% body mass as plastic in the gut: yes, documented in some wildlife contexts; associated with measurable harm and sometimes high mortality risk.

• 1–2% of tissues being plastic: not supported by current evidence.

• High-dose microplastic exposure experiments: show plausible mechanisms of harm, but translating that to real-world “percent plastic” body burdens is not straightforward.