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.

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.

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.

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.

Figure 1:

Raman spectra collected on the microplastics most commonly occurring in the analyzed samples.

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