TOXIC METALS, CANCER RISK AND GENOTOXICITY BIOMARKERS IN HUMANS EXPOSED TO ELECTRONIC WASTE IN SOUTHWESTERN NIGERIA

Abstract

The scourge of electronic waste (e-waste) is currently a major global concern, particularly in developing countries like Nigeria where its reprocessing is substantial but unregulated. The possible contribution of e-waste toxic metals to the risk of cancer development in Nigeria has received little attention. This study was aimed at assessing the exposure of Nigerians to toxic metals in e-waste, using biomarkers of exposure and genotoxicity to evaluate the risk of cancer development. In this cross-sectional study, 632 consenting participants were enrolled from Benin, Lagos and Ibadan, Southwestern Nigeria; consisting of 381 e-waste workers (EW) and 120 environmental e-waste exposed participants (EEEP) age-matched with 131 unexposed participants (control). Blood (10 mL) was obtained from each participant. Levels of toxic metals (cadmium, lead, mercury, arsenic, chromium, nickel, molybdenum, aluminium, vanadium, thallium, antimony and tin) in blood and essential metals (zinc, selenium, copper and cobalt) in serum were determined using inductively coupled plasma-mass spectrometry. Vitamins A, C and E, oxidative stress biomarkers: malondialdehyde and uric acid (UA), activities of enzymatic antioxidants [catalase, superoxide dismutase (SOD), ɣ-glutamyltransferase (GGT) and glutathione peroxidase (GPx)] were determined in serum using standard methods like spectrophotometry. Genotoxicity biomarkers; [wild-type tumour suppressor protein (wt-p53), 8-oxoguanine-DNA glycosylase (OGG1), and 8-hydroxy-2ʹ-deoxyguanosine (8-OHdG)]; glutathione (GSH) and tumour markers [prostate-specific antigen (PSA) and alpha-fetoprotein] in serum were determined using ELISA. Micronucleus assay was carried out using microscopy. Data were analysed using ANOVA and Pearson’s correlation coefficient at α0.05. Elevated levels of toxic metals (cadmium, lead, mercury, arsenic, chromium, nickel, molybdenum, aluminium, vanadium, and thallium) and decreased levels of zinc, selenium, copper and cobalt were observed in both EW and EEEP compared with control. Vitamins A and C in EEEP (2.20±0.04 µmol/L; 116±2.03 µmol/L) were higher than EW (2.08±0.04 µmol/L; 88.75±3.33 µmol/L) and control (1.97±0.09 µmol/L; 92.19±1.68 µmol/L), respectively while vitamin E in EW (8.91±0.19 µmol/L) and EEEP (8.05±0.18 µmol/L) were lower than control (12.36±0.34 µmol/L). Malondialdehyde and UA levels were raised in EW and EEEP compared with control, while GSH was higher in control (5.41±0.09 µmol/L) than EEEP (4.44±0.09 µmol/L) and EW (3.96±0.91 µmol/L). Catalase, SOD and GPx activities were decreased in EW (122.83±3.54; 140.00±6.32; 31.41±0.84 µmol/min/mL) and EEEP (123.84±2.77; 188.31±8.79; 33.46±0.46 µmol/min/mL) compared with control (215.74±4.55; 328.48±20.44; 39.90±0.26 µmol/min/mL) respectively, while GGT activity was higher in EW and EEEP than control. The levels of wt-p53 in EW (0.450.05 ng/mL) and EEEP (0.410.04 ng/mL) were lower than control (0.730.12 ng/mL), while OGG1 activity in EEEP (0.35±0.04 ng/mL) was higher than EW (0.24±0.03 ng/mL) and control (0.23±0.05 ng/mL). The levels of 8-OHdG in EW (127.8218.29 pg/mL), EEEP (126.5314.01 pg/mL) and control (95.955.60 pg/mL) were similar. The PSA and alpha-fetoprotein in EW (7.61±1.93 µg/L; 5.62±0.32 µg/L) were more elevated than EEEP (3.51±0.27 µg/L; 3.34±0.22 µg/L) and control (2.80±0.24 µg/L; 3.56±0.20 µg/L), respectively. The MnPCE/1000PCE in EW (22.7±0.15) was higher compared with EEEP (4.17±0.28) and control (0.99±0.76). Nigerians exposed to toxic metals in e-waste experienced decreased levels of micronutrients, downregulation of wt-p53 and increased DNA damage which may lead to increased cancer risk.