Invisible but Insidious Effects of Microplastics

Abstract

Increasing evidence on the adverse health impacts of microplastics (MPs) is available, but their associated risks to the well-being of humans and long-term impacts are poorly understood. An indicator of the remote effects of MPs may be their influence on the rate of aging. To assess the effects of MPs on the aging process, we used accelerated senescence OXYS rats that develop a complex of geriatric diseases. We prepared the polyethylene terephthalate MPs (2-6 microns in size) and in OXYS and Wistar (maternal strain) rats assessed the influence of chronic administration of MPs (10 or 100 mg/kg per day from age 1.5 to 3.5 months,) on the hematological and biochemical blood parameters, spatial learning, and memory. In addition, the effects of MPs on the development of cataracts and retinopathy, similar to age-related macular degeneration (AMD), in OXYS rats were assessed. We found that in the absence of significant changes in standard clinical blood parameters, chronic MP administration negatively affected the cognitive functions of both Wistar rats and OXYS rats. Additionally, a dose of 100 mg/kg MPs contributed to cataract and AMD progression in OXYS rats. Our results suggest that MPs may increase the rate of aging and, in the long term, lifespan.

Keywords: Alzheimer’s disease; OXYS rats; age-related macular degeneration; cognitive ability; memory; microplastic; polymers.

Figure 1

Characterization of the obtained particles: (A) SEM image; (B) FTIR spectra of the PET particles: initial film (solid line) and microparticles (dotted line).

Figure 2

Effect of MPs on cataract (A) and retinopathy (B) development in OXYS rats. The data are presented as the distribution of the eyes of the animals within the cataract stages and signs of AMD-like pathology development in the control and MP-exposed OXYS rats. 1–3—corresponding stage of the disease.

Figure 3

Barnes maze performance of MP-exposed and control OXYS and Wistar rats. Analysis of (A) the distance travelled by the rats to locate the escape box and (B) their speed. OXYS rats travelled a shorter distance to escape and at a slower speed than did Wistar rats. On day 1, the distance travelled and speed of MP-exposed Wistar rats at a dose of 100 mg/kg were significantly lower than those of control Wistar rats. The numbers of (C) holes and (D) heads dipping from the table on the first day of Barnes performance before training. The control OXYS rats and MP-exposed rats of both strains presented lower exploratory activity than the control Wistar rats did (*, Newman–Keuls post hoc test; p < 0.05). (E) The primary latency was longer in OXYS rats than in Wistar rats. The data are presented as the means ± SEMs, n = 9–10. In (A,B,E), * p < 0.05 for differences between control OXYS and Wistar rats; # p < 0.05 for an effect of MP exposure. The circles in (C,D) indicate the individual scores of each rat.

Figure 4

Cognitive performance of MP-exposed and control OXYS and Wistar rats in the Barnes maze. (A) Representative between-group comparison of profiles of strategy selection by each group for the entire training session (prior to probe). (B) A comparison of the summed cognitive indices for the training trials revealed that control OXYS rats and MP-exposed rats of both strains had significantly lower scores than control Wistar rats did (*, Newman–Keuls post hoc test; p < 0.05). (C) Percentage of time spent in the target quadrant during the probe trial. (D) Profiles of strategy selection by each group for the probe trial. The data are presented as the means ± SEMs; n = 9–10. In (B), * p < 0.05 for differences between control OXYS and Wistar rats and for an effect of MP exposure in Wistar rats. The circles in (B,C) indicate the individual scores of each rat.

Figure 5

Schematic description of the method used to produce PET microparticles.