In late May 2021, off the coast of Colombo, Sri Lanka, the ship fire and subsequent plastic spill of the M/V X-Press Pearl released ~1680 tons of plastic nurdles and other plastic debris, making it the largest maritime plastic spill in history. Along with polyethylene pellets, the cargo on the ship included an assortment of raw materials, hazardous chemicals, and finished products, 4 capable of creating a complex mixture of uncertain toxicity. An observable fraction of the spilled material included burnt plastic (pyroplastic), formed during the events of the ship fire. The pyroplastic was heterogeneous in size and shape and somewhat friable, giving it a greater propensity to form secondary microplastics than the other spilled material. The attributes of the pyroplastic collectively challenged the response efforts and elevated the plastic's potential for injury to a host of marine organisms. At least five forms of plastic were released, including three types of nurdles distinguished by their color (white, orange, and gray) and two types of pyroplastic characterized by their shape and size (burnt plastic and combustion remnants) (Figure ). 7,9,10 Pieces of pyroplastic were not only at least 3-fold more chemically complex because of the fire, 4 they were shown to have the greatest content of polycyclic aromatic hydrocarbons (PAHs) of any plastic marine debris recorded to date, 199,000 ng/g. Comparatively, the more abundant white nurdles had PAH contents less than ~2,500 ng/g, within the range of other marine debris. PAHs are chemical pollutants, many of which are carcinogenic, raising concern over the release of pyroplastic into the environment. While substantial, PAHs constituted only a fraction of the chromatographic features resolved within solvent extracts of the material. No phthalates have been detected. However, several other tentatively identified compounds have included chemical additives (e.g., Irgafos 168, 1,3,5tris(2,4-di-t-butylphenyl)phosphite 4 ; and Bumetrizole (Tinuvin-326), 2-(2-Hydroxy-3-t-butyl-5methylphenyl)-5-chlorobenzotriazole ), their thermal breakdown products (e.g., 2,4-di-tbutylphenol), and metals (e.g., Ti, Zn, Mn, Co) as well as unknown compounds, demonstrating that the pyroplastic included a complex mixture of compounds, many with unknown bioactivity. Figure . The spilled plastic included white nurdles (A), orange nurdles (B), gray nurdles (C), pieces of burnt plastic (D), and larger combustion remnant chunks (E). Reprinted from James et al. (CC BY-NC-ND 4.0). While the M/V X-Press Pearl disaster was a localized, acute release of pyroplastics, these forms of plastic have been documented globally. Along with other forms of charred plastic, pyroplastics have been found on coastlines and in waterbodies in Africa, Antarctica, Asia, Europe, North America, and South America (Figure ). To date, the limited chemical analyses performed for beached pyroplastics unrelated to the M/V X-Press Pearl disaster have shown that these materials can be enriched in metals, PAHs, and phthalates. Pyroplastics are an emerging global contaminant thought to primarily enter the marine environment following fires at the wildland-urban interface and leaking of openly burned waste. The toxicological concerns for burning plastic are not new, as emphasized by studies of the toxicity and chemistry of smoke and ash from residential and commercial fires, military burn pits, openly burned municipal waste, landfill fires, and fires at the wildland-urban interface as well as firewater runoff (the contaminated water produced during firefighting). However, these studies have not investigated the bioactivity of burnt plastic that remained after the fires were extinguished; their focus has largely been on aerosols and their impacts on air quality and human health. Similarly, despite their documented presence globally and unlike other plastic debris, the bioactivity of any pyroplastic is yet to be assessed. Not only is an assessment of potential toxicity necessary for making a hazardous waste determination of the spilled plastic, 9 but there is also a need to measure its bioactivity owing to the friability of the pyroplastic, the elevated amounts of PAHs and other chemicals that can be associated with the pyroplastic, and the recognized "Trojan horse" effect for microplastic and nanoplastics to leach chemical pollutants to biota upon exposure (e.g., ingestion). Reporter bioassays have been a valuable method for determining the bioactivity of a chemical or complex mixture. Targeted bioassays have been used to screen extracts and leachates from consumer plastics, plastic photoproducts, weathered plastics, and combustion-derived particulate matter and ash, Measurements have primarily focused on the activation of the aryl hydrocarbon receptor (AhR), estrogen receptor (ER), androgen receptor (AR), pregnane X receptor (PXR), peroxisome proliferator-activated receptors (PPAR), and markers for oxidative stress (NRF2). Though targeted bioassays have been valuable, high-throughput, non-targeted screens of over 50 end points using the Attagene FACTORIAL platform can provide a more comprehensive assessment of bioactivity, capable of assigning chemicals and complex mixtures to specific modes of action. Additionally, as part of the United States Environmental Protection Agency (EPA) ToxCast program, the FACTORIAL platform has been used to evaluate more than 3000 chemicals, making it possible to compare bioactivities against an extensive database of diverse compounds. Moreover, variations of the platform (i.e., EcoTox and AquaTox) enable a harmonized cross-species assessment of endocrine and metabolic disruption upon chemical exposure for humans and wildlife (mouse, zebrafish, medaka, rainbow trout, chicken, frog, and turtle). Having such capabilities is valuable to addressing the potential ecotoxicity of pyroplastics. Recent work uncovering the acute toxicity of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and its oxidized form (6PPD-quinone) to select salmonids and not others emphasizes the need to assay across phylogenetically separated species when assessing the potential ecotoxicity of plastic-associated chemicals. This is particularly needed for the M/V X-Press Pearl disaster as Sri Lankan fisheries rely on numerous, diverse fish species for sustenance. Herein, three FACTORIAL bioassays were used to assess the bioactivity of solvent extracts of white nurdles and pyroplastic collected within days of, and 242 days after, the M/V X-Press Pearl disaster. In total, the activities of 70 end points were measured, assessing the induction of human transcription factors and nuclear receptors related to biotransformation, lipid metabolism, the endocrine system, immunity, and cell stress, differentiation, and growth. Additionally, the AquaTox bioassay assessed 6-7 end points for endocrine and lipid metabolic function for each of three phylogenetically distinct fish species. Our findings provide needed information to guide long-term monitoring efforts, make hazard assessments of the spilled material, and direct further research on pyroplastics, an emerging global contaminant.