The investigators recent study has found that ambient melamine exposure can cause the increase of biomarkers of renal tubular injury in melamine manufacturing workers. Thus, in this year, the investigators will examine whether the intervention by installing ventilation in the workplace and providing personal protective equipment and education can decrease ambient melamine exposure and further decrease urinary biomarkers of renal tubular injury such as N-acetyl β-D-glucosaminidase (NAG) and β2-microglobulin (β2-MG).

The investigators through intervention trial design to examine whether the use of ventilation in the workplace can decrease ambient melamine exposure, oxidative stress markers (such as 8-hydoxy-2-deoxyguanosine, malondialdehyde)and indicators of early renal damage (such as N-acetyl β-D-glucosaminidase, microalbumin and β2-microglobulin). The one week before intervention and the second week after intervention, the volunteers were asked to collect their urine samples for one consecutive week during mornings and afternoons. Blood samples were taken on Fridays morning, workplace air was sampled for 5 consecutive days. Then the investigators continued to trace the melamine concentration change of volunteers and workplace every three-month intervals after intervention, and blood samples were taken on 12th and 24th month.

Inclusion Criteria:

• healthy adult over age of 20 years

Exclusion Criteria:

• any hormone treatment or major chronic diseases (such as: cancer, hypertension, diabetes, chronic kidney disease and chronic liver disease) and patients with urinary calculi or family history of urinary calculi

Blinded by lab. persons who analyzed biomarkers