Investigation Of Oxidative Stress In Peripheral Blood Of Workers Occupationally Exposed To Hexavalent Chromium

1 ObjectivesChromium compounds,as heavy metals,are commonly environmental pollutants. Chromium compounds are used in some industries,for example,electroplating, metallurgy,leather and so on,which can produce "three wastes".Those environmental pollutants can affect the health of occupational and non-occupational exposure populations.The toxicity of chromium compounds is related to the valence.The chromium compounds,as trivalent chromium,exist in food and biological tissue.Also chromium is one of essential trace elements of human body.Hexavalent chromium can induce sensitive and corrosive effects on skin and mucosa resulting in dermatitis, chrome sores,asthma and nasal septum perforation,liver damage,kidney damage, heart damage and reproductive toxicity.People pay more attention to the risk of health for the workers occupationally exposed to low concentrations chromium due to the hazards to health of hexavalent chromium compounds.Therefore,it is necessary to find some reliable biomarkers to assess the exposure levels and effects of chromium compounds.So far,a lot of investigations for the chromium biomarker have been carried out. The results of some studies showed that the concentrations of serum SOD,GSH-Px and GST in population exposed to Cr were significantly higher than those in controls, which indicated that chromium can cause the increase of lipid peroxidation products and susceptibility to oxidative stress,and decrease the antioxidation ability.For this reason,the aims of present study were to investigate the levels of oxidative stress in worker occupationally exposed to hexavalent chromium and to explore the possibility that the indexes of oxidative stress serve as the early effective biomarkers of chromium exposure.2 Subjects and Methods2.1 Subjects The exposure group consisted of 124 workers(male 100,female 24), occupationally exposed to Cr,who were from the Electroplating enterprises factories. The average age of the workers was 38.76±9.09 years old(from 21 to 62 years old). The average duration of service was 55.17±51.83 months(from 1 month to 20 years). The average duration of service in most workers(76.61%) was between 1 to 10 years. The control group consisted of 41 healthy subjects(male 17,female 14) in the same city,who never exposed to hazardous substances and heave metals.The average age of controls was 39.34±10.765 years old(from 20 to 63 years old).There was no significant difference between exposure group and control group for age and sex (X~2=3.482,P=0.062).2.2 Methods2.2.1 Detecting the air Cr concentration in the workshopsThe air samples were collected in the workshops where the workers were working. The short time sampling method was used to mom'tor the air Cr concentration in the workshops,according to GBZ 159-2004(5L/min for 15 min.each time).The concentration of Cr was measured by Flame atomic absorption spectrometry for all samples.2.2.2 Collecting the blood samples All used containers were treated with nitric acid to avoid chromium and other heavy metals pollution.After physical examination,10 ml peripheral blood collected from each subject was treated with EDTA for anticoagulation,and divided into two tubes,one for the detection of chromium,the other for centrifugal separation of plasma to be kept at -20℃.2.2.3 Detecting blood chromiumThe blood Cr was measured by Graphite furnace atomic absorption spectrometry.2.2.4 Detecting the levels of oxidative stress in peripheral bloodThe concentration of MDA and the activities of SOD,CAT and GST were measured by Spectrophotometry using 721 spectrophotometer.The reagent kits used were provided by Nanjing Jiancheng Institute of Biological Engineering.The examinations were performed according to the instruction of reagent kits.3 Results3.1 Internal and external exposure levels of chromiumThe external exposure level of workers occupationally exposed to hexavalent chromium:The average air chromic concentration in workshops was 0.010±0.013mg/m~3(0.005 - 0.06mg/m~3).The only one highest air chromic TWA concentration in workshops was 0.06mg/m~3,which was slightly higher than the criteria of the National Occupational Health Standards(0.05mg/m~3).And the remaining samples air chromic TWA and STEL concentration-did not exceed the criteria of the National Occupational Health Standard.The average air chromic concentration in workshops was lower than the criteria of the National Occupational Health Standards. The internal exposure dose of workers occupationally exposed to Cr:The average blood Cr concentration of exposure group was 2.76±3.58ug/L,the average blood Cr concentration of control group was 2.02±2.21ug/L.The difference of the mean blood Cr level between exposure group and control group was not significant(P＞0.05). 3.2 The Detection of oxidative stress for occupational workers exposed to hexavalent chromiumThe 95%confidence intervals for MDA and SOD in control group were 6.66-10.42 mmol/L and 59.39-68.85 KU/L,respectively.The 95%confidence intervals for MDA and SOD in Cr exposure group were 8.92-12.70 mmol/L and 38.04-43.54 KU/L,respectively.Although the mean blood MDA value in Cr exposure group was 10.81±10.59 mmol/L which was higher than the mean blood MDA value(8.54±5.96 mmol/L) in control group,there was no significant difference between exposure group and control group(P=0.055).However,the mean blood MDA values in the exposure group with higher blood Cr(≧3ug/L) and the exposure group with longer service duration(≧11 years) were 14.19±11.94 mmol/L and 20.90±16.88 mmol/L, which were significantly higher than the mean blood MDA value in control group(P＜0.01). The mean blood SOD value in Cr exposure group was 40.79±15.41 KU/L which was significantly higher than the mean blood SOD value(64.12±14.98 KU/L) in control group (P＜0.01).There was no significant difference between Cr exposure group and control group for blood CAT and GST(P＞0.05).4 ConclusionThe mean blood SOD value in Cr exposure group was significantly higher than the mean blood SOD value in control group,also the mean blood MDA values in the exposure groups with higher blood Cr and with longer service duration were significantly higher than the mean blood MDA value in control group.The results of present study indicated the possibility that the blood MDA and SOD serve as the early effective biomarkers of chromium exposure in future.