Plastic pollution became a main challenge for human beings as demonstrated by the increasing dispersion of plastic waste into the environment. Microplastics (MPs) have become ubiquitous and humans ...are exposed daily to inhalation or ingestion of plastic microparticles. Recent studies performed using mainly spectroscopy or spectrometry-based techniques have shown astounding evidence for the presence of MPs in human tissues, organs and fluids. The placenta, meconium, breast milk, lung, intestine, liver, heart and cardiovascular system, blood, urine and cerebrovascular liquid are afflicted by MPs’ presence and deposition. On the whole, obtained data underline a great heterogeneity among different tissue and organs of the polymers characterized and the microparticles’ dimension, even if most of them seem to be below 50–100 µm. Evidence for the possible contribution of MPs in human diseases is still limited and this field of study in medicine is in an initial state. However, increasing studies on their toxicity in vitro and in vivo suggest worrying effects on human cells mainly mediated by oxidative stress, inflammation and fibrosis. Nephrological studies are insufficient and evidence for the presence of MPs in human kidneys is still lacking, but the little evidence present in the literature has demonstrated histological and functional alteration of kidneys in animal models and cytotoxicity through apoptosis, autophagy, oxidative stress and inflammation in kidney cells. Overall, the manuscript we report in this review recommends urgent further study to analyze potential correlations between kidney disease and MPs’ exposure in human.
Abstract
Background and Aims
Microplastics (MPs), plastic fragments less than 5mm in diameter, have been recognized as a global environmental issue. Various studies have shown their ubiquitous ...presence and their toxicity on marine and terrestrial fauna. Currently in humans, the presence of MP has been evidenced in lungs, placenta, blood, and liver. However, there is still very little knowledge about their presence in different organs and tissues and their prospective toxicity. The objective of this study was to investigate the presence of microplastics in human kidneys and urine.
Method
We obtained 10 urine samples from healthy individuals and 10 kidney healthy tissue samples from nephrectomies in renal cancer The detection and characterization of microplastics was performed by a light microscope (Leica, total magnification of 500x) coupled to a Raman spectrometer (Renishaw System 2000). To this purpose, specimens were digested by a 10% KOH solution at 60°C and subsequently filtered on membrane filters with micropores of 0.2 μm to retain possible particles. This procedure was performed adopting a “plastic-free” protocol. Procedural blanks were performed as controls using the same protocol. To determine the nature of the detected particles, Raman spectra were compared to the ones present in the Renishaw spectrometer database (inorganic materials, polymers and forensic materials) i, in the SLOPP Library of Microplastics ii, and in the IRUG Spectral Database (pigments section) iii. A home-developed software was employed to compare spectra. Data analysis was performed by using the statistical software package Prism6 (Graphpad Software) Chi-square test, Student's t-test were performed to compare data accordingly. The significance threshold was set at p < 0.05.
Results
17 fragments (mean 1,7±2,11/sample) were identified and characterized on 7 out of 10 human kidney samples. The result was significant (p.value 0.041) compared with controls (mean 0,33±0,49/blank). 9 fragments were identified and characterized on 7 out of 10 human urine sample (mean 1.28±0,49/sample) highly significant (p.value 0.0002). Spectra analyzed by microRaman showed the presence polymers, polymers additives and pigments associated to polymers such as: hematite, Cu- phthalocyanine blue, Cerulean Blue, Polystyrene, Styrene-Isoprene and polyethylene.
Conclusion
We first demonstrated the presence of MPs in human kidneys, and we also confirm their presence in urine assuming the presence of a kidney clearance mechanism. Using Raman Microspectroscopy, it was also possible to determine the nature and quantity of MPs. The remarkable relevance of this identification, potentially concern much of the humans, deserve a widespread attention of the medical community for its potential implications. Further studies are urgently needed to investigate the possible nephrotoxicity of MPs, mechanisms of kidney clearance and tissue accumulation.
