Toxicological assessment of dietary exposure of polyethylene microplastics on growth, nutrient digestibility, carcass and gut histology of Nile Tilapia (Oreochromis niloticus) fingerlings.

This study was conducted to ascertain the negative effects of dietary low-density polyethylene microplastics (LDPE-MPs) exposure on growth, nutrient digestibility, body composition and gut histology of Nile tilapia (Oreochromis niloticus). Six sunflower meal-based diets (protein 30.95%; fat 8.04%) were prepared; one was the control (0%) and five were incorporated with LDPE-MPs at levels of 2, 4, 6, 8 and 10% in sunflower meal-based diets. A total of eighteen experimental tanks, each with 15 fingerlings, were used in triplicates. Fish were fed at the rate of 5% biomass twice a day for 60 days. Results revealed that best values of growth, nutrient digestibility, body composition and gut histology were observed by control diet, while 10% exposure to LDPE-MPs significantly (P < 0.05) reduced weight gain (WG%, 85.04%), specific growth rate (SGR%, 0.68%), and increased FCR (3.92%). The findings showed that higher level of LDPE-MPs (10%) exposure in the diet of O. niloticus negatively affects nutrient digestibility. Furthermore, the results revealed that the higher concentration of LDPE-MPs (10%) had a detrimental impact on crude protein (11.92%) and crude fat (8.04%). A high number of histological lesions were seen in gut of fingerlings exposed to LDPE-MPs. Hence, LDPE-MPs potentially harm the aquatic health.

Assessment of perfluorocarboxylic acids in fluorinated high-density polyethylene containers and estimation of potential non-cancer risks associated with anticipated use scenarios.

High density polyethylene (HDPE) containers are fluorinated to impart barrier properties that prevent permeation of liquid products filled in the container. The process of fluorination may result in the unintentional formation of certain per- and polyfluoroalkyl substances (PFAS), specifically perfluoroalkyl carboxylic acids (PFCAs), as impurities. This study measured the amounts of PFCAs that may be present in the fluorinated HDPE containers, which could migrate into products stored in these containers. Migration studies were also conducted using water and mineral spirits to estimate the amount of PFCAs that might be found in the products stored in these containers. The migration results were used to conservatively model potential PFCA exposures from use of six product types: indoor-sprayed products, floor products, hand-applied products, manually-sprayed pesticides, hose-end sprayed products, and agricultural (industrial) pesticides. The potential that such uses could result in a non-cancer hazard was assessed by comparing the modeled exposures to both applicable human non-cancer toxicity values and environmental screening levels. Environmental releases were also compared to aquatic and terrestrial predicted no-effect concentrations (PNECs). The results of these analyses indicated no unreasonable non-cancer risk to humans, aquatic species, and terrestrial species from PFCAs in products stored in fluorinated HDPE containers.

Multi-biomarkers hazard assessment of microplastics with different polymers by acute embryo test and chronic larvae test with zebrafish (Danio rerio).

Microplastics as emerging contaminants show various composition features in the environment. However, influence of polymer types on the toxicity of microplastics is still unclear, thus affecting evaluation of their toxicity and ecological risks. In this work, toxic effects of microplastics (fragment, 52-74 µm) with different polymer types including polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP) and polystyrene (PS) to zebrafish (Danio rerio) were studied using acute embryo test and chronic larvae test. Silicon dioxide (SiO2) was used as a control representing natural particles. Results showed microplastics with different polymers had no influence on embryonic development at environmental relevant concentration (102 particles/L), but could lead to accelerated heartbeat rate and increased embryonic death when exposed to SiO2, PE and PS at higher concentrations (104 and 106 particles/L). Chronic exposure for zebrafish larvae indicated different polymers of microplastics did not affect zebrafish larvae' feeding and growth, nor induce oxidative stress. But larvae' locomotion level and AChE (acetylcholinesterase) activities could be inhibited by SiO2 and microplastics at 104 particles/L. Our study demonstrated negligible toxicity of microplastics at environmental relevant concentration, while different polymers of microplastics have similar toxic effects as SiO2 at high concentrations. We suggest that microplastic particles may have the same biological toxicity as natural particles.

Toxicity assessment of polyethylene microplastics in combination with a mix of emerging pollutants on Physalaemus cuvieri tadpoles.

Studies in recent years have shown that aquatic pollution by microplastics (MPs) can be considered to pose additional stress to amphibian populations. However, our knowledge of how MPs affect amphibians is very rudimentary, and even more limited is our understanding of their effects in combination with other emerging pollutants. Thus, we aimed to evaluate the possible toxicity of polyethylene MPs (PE-MPs) (alone or in combination with a mix of pollutants) on the health of Physalaemus cuvieri tadpoles. After 30 days of exposure, multiple biomarkers were measured, including morphological, biometric, and developmental indices, behavioral parameters, mutagenicity, cytotoxicity, antioxidant and cholinesterase responses, as well as the uptake and accumulation of PE-MPs in animals. Based on the results, there was no significant change in any of the parameters measured in tadpoles exposed to treatments, but induced stress was observed in tadpoles exposed to PE-MPs combined with the mixture of pollutants, reflecting significant changes in physiological and biochemical responses. Through principal component analysis (PCA) and integrated biomarker response (IBR) assessment, effects induced by pollutants in each test group were distinguished, confirming that the exposure of P. cuvieri tadpoles to the PE-MPs in combination with a mix of emerging pollutants induces an enhanced stress response, although the uptake and accumulation of PE-MPs in these animals was reduced. Thus, our study provides new insight into the danger to amphibians of MPs coexisting with other pollutants in aquatic environments.

Assessment of acute toxicity and developmental transformation impacts of polyethylene microbead exposure on larval daggerblade grass shrimp (Palaemon pugio).

Due to the ubiquity of microplastic contamination in coastal waters, there is potential for adverse impacts to organism development. One organism of interest is the daggerblade grass shrimp, Palaemon pugio, an ecologically important species in estuaries along the east coast of North America. We exposed larval grass shrimp to virgin polyethylene microbeads (35 and 58 µm) at a high (0.375 and 1.95 mg/L), medium (0.0375 and 0.195 mg/L), and a low concentration (0.00375 and 0.0195 mg/L), respectively for 23 days to assess mortality, transformation time from larval to juvenile stage, and weight. Average percent mortality was 3.7 to 4.8 times higher in the experimental treatments compared to controls. The greatest proportion of mortality was observed in the first 11 days. Median time for transformation ranged from 20.2 to 20.8 days. Shrimp exposed to the 35 µm beads in the high treatment (20.2 days) transformed significantly faster than the control shrimp (20.8 days). Although development was not delayed and size of the shrimp did not differ, the acute toxicity of microplastics on grass shrimp is a concern due to their role in energy cycling within tidal-creeks. These findings suggest potential population and community level effects following microplastic exposure.

A multifaceted assessment of the effects of polyethylene microplastics on juvenile gilthead seabreams (Sparus aurata).

Plastic pollution has become a major environmental and societal concern in the last decade. From larger debris to microplastics (MP), this pollution is ubiquitous and particularly affects aquatic ecosystems. MP can be directly or inadvertently ingested by organisms, transferred along the trophic chain, and sometimes translocated into tissues. However, the impacts of such MP exposure on organisms' biological functions are yet to be fully understood. Here, we used a multi-diagnostic approach at multiple levels of biological organization (from atoms to organisms) to determine how MP affect the biology of a marine fish, the gilthead seabream, Sparus aurata. We exposed juvenile seabreams for 35 days to spherical 10-20 µm polyethylene primary MP through food (Artemia salina pre-exposed to MP) at a concentration of 5 ± 1 µg of MP per gram of fish per day. MP-exposed fish experienced higher mortality, increased abundance of several brain and liver primary metabolites, hepatic and intestinal histological defects, higher assimilation of an essential element (Zn), and lower assimilation of a non-essential element (Ag). In contrast, growth and muscle C/N isotopic profiles were similar between control and MP-exposed fish, while variable patterns were observed for the intestinal microbiome. This comprehensive analysis of biological responses to MP exposure reveals how MP ingestion can cause negligible to profound effects in a fish species and contributes towards a better understanding of the causal mechanisms of its toxicity.

Preliminary Assessment on the Histological Changes in Juvenile Siganus guttattus (Bloch, 1787) Exposed to Plastic Debris.

Plastic debris is ubiquitous in the marine environment and many of this is polyethylene based plastic bags. Its potential effect on marine organisms is still understudied. Hence, this study determined the histological changes induced in the intestine and liver of the juvenile rabbit fish, Siganus guttatus. S. guttatus (N = 150) were sub chronically exposed to plastic bag debris suspensions (0, 0.01, 0.1, 1.0 and 10 mg L-1) for 10 days. In addition to histological changes, the condition factor (CF) index of the fishes were assessed. Results showed that there was no significant difference in the CF index of the fishes exposed to varying concentrations of plastic suspensions, there was however histological changes in fishes exposed to 10 mg L-1. The histological changes in the intestine were hyperemia, necrosis, goblet cells hyperplasia, and shortening of the villi. Histological changes in the liver were hyperemic blood vessels and vacuolization. Fishes exposed to 10 mg L-1 exhibited a higher proximal, distal, liver and total organ index as compared to those unexposed (p < 0.05).

Assessment of Transcriptomic and Apical Responses of Daphnia magna Exposed to a Polyethylene Microplastic in a 21-d Chronic Study.

There is global concern regarding the fate and effects of microplastics in the environment, particularly in aquatic systems. In the present study, ethylene acrylic acid copolymer particles were evaluated in a chronic toxicity study with the aquatic invertebrate Daphnia magna. The study design included a natural particle control treatment (silica) to differentiate any potential physical effects of a particle from the intrinsic toxicity of the test material. In addition to the standard endpoints of survival, growth, and reproduction, the transcriptomic profiles of control and ethylene acrylic acid copolymer-exposed D. magna were evaluated at the termination of the 21-d toxicity study. No significant effects on D. magna growth, survival, or reproduction were observed in comparison with both particle and untreated control groups. Significant transcriptomic alterations were induced at the highest treatment level of 2.3 × 1012 particles of the ethylene acrylic acid copolymer/L in key pathways linked to central metabolism and energy reserves, oxidative stress, and ovulation and molting, indicating a global transcriptomic response pattern. To put the results in perspective is challenging at this time, because, to date, microplastic environmental monitoring approaches have not been equipped to detect particles in the nanosize range. However, our results indicate that ethylene acrylic acid copolymer microplastics in the upper nanosize range are not expected to adversely affect D. magna growth, survival, or reproductive outcomes at concentrations of up to 1012 particles/L. Environ Toxicol Chem 2020;39:1578-1589. © 2020 SETAC.

Final report on the safety assessment of polyethylene.

Polyethylene is an ethylene polymer used for a variety of purposes in cosmetics as an abrasive, adhesive, binder or bulking agent, an emulsion stabilizer, a film former, an oral care agent, and as a nonaqueous viscosity-increasing agent. Polyethylene is also used in food packaging materials and medical products, including prosthetics. The molecular weight of Polyethylene as used in cosmetics varies over a wide range. The lowest reported molecular weight is 198 Daltons and the highest is 150,000. In any given polymer preparation, there can be a broad range of molecular weights. Cellular and tissue responses to Polyethylene, determined as part of implant biocompatibility testing, include fibrous connective tissue build-up around the implant material that varies as a function of the physical form of the implant material. Specific assays for osteoblast proliferation and collagen synthesis demonstrated a reduction as a function of exposure to Polyethylene particles that is inversely related to particle size. The effect of Polyurethane particles on monocyte-derived macrophages, however, had a stimulatory effect, prolonging the survival of these cells in culture. The LD50 for Polyethylene, with an average molecular weight of 450, in rats was > 2000 mg/kg. For Polyethylene with an average molecular weight of 655, the LD50 was > 5.0 g/kg. Toxicity testing in rats shows no adverse effects at Polyethylene (molecular weight not given) doses of 7.95 g/kg or at 1.25%, 2.50%, or 5.00% in feed for 90 days. Dermal irritation studies on rabbits in which 0.5 g of Polyethylene (average molecular weight of 450) was administered in 0.5 ml of water caused no irritation or corrosive effects; Polyethylene with an average molecular weight of 655 was a mild irritant. Polyethylene (average molecular weight of 450) did not cause dermal sensitization in guinea pigs tested with 50% Polyethylene (w/w) in arachis oil BP. Polyethylene, with a molecular weight of 450 and a molecular weight of 655, was a mild irritant when tested as a solid material in the eyes of rabbits. Rabbit eyes treated with a solution containing 13% Polyethylene beads produced minimal irritation and no corneal abrasions. No genotoxicity was found in bacterial assays. No chemical carcinogenicity has been seen in implantation studies, although particles from Polyethylene implants can induce so-called solid-state carcinogenicity, which is a physical reaction to an implanted material. Occupational case reports of ocular irritation and systemic sclerosis in workers exposed to Polyethylene have been difficult to interpret because such workers are also exposed to other irritants. Clinical testing of intrauterine devices made of Polyethylene failed to conclusively identify statistically significant adverse effects, although squamous metaplasia was observed. The Cosmetic Ingredient Review (CIR) Expert Panel did not expect significant dermal absorption and systemic exposure to large Polyethylene polymers used in cosmetics. The Panel was concerned that information on impurities, including residual catalyst and reactants from the polymerization process, was not available. The Panel considered that the monomer unit in Polyethylene polymerization is ethylene. In the United States, ethylene is 99.9% pure. The other 0.1% includes ethane, propylene, carbon dioxide, carbon monoxide, sulfur, hydrogen, acetylene, water, and oxygen. The Panel believed that the concentration of these impurities in any final polymer would be so low as to not raise toxicity issues. Safety tests of cosmetic-grade Polyethylene have consistently failed to identify any toxicity associated with residual catalyst. Although it was reported that one process used to cross-link Polyethylene with an organic peroxide, this process is not currently used. In addition, cosmetic-grade Polyethylene is not expected to contain toxic hexanes. The Panel was concerned that the only genotoxicity data available was nonmammalian, but taking this information in concert with the absence of any chemical carcinogenicity in implant studies suggests no genotoxic mechanism for carcinogenicity. The solid-state carcinogenicity effect was not seen as relevant for Polyethylene as used in cosmetics. The available data support the conclusion that Polyethylene is safe for use in cosmetic formulations in the practices of use and concentrations described.