Finger nail fluoride guideline for hydrogen fluoride exposure

INTRODUCTION: In September 27, 2012, approximately 8 tons of anhydrous hydrofluoric acid leaked by accident in Gumi, Korea. An emergency epidemiology study was conducted after two weeks. Almost ingested fluorides (F) are accumulated in hard tissues and finger nail is known as a biomarker for acute and chronic exposure to F. However there is no guideline for HF exposure using finger nail. Hence this study aims to suggest the guideline for HF exposure using finger nail and assess the exposure amount of HF of the residents.

METHODS: Clinical examination including oral examination was conducted among 1353 of residents. Thumb nails were collected at the baseline examination, and 2.5, 3.0, 3.5, 4.0, 4.5 months after the accident. Sociodemographic information was collected by questionnaire and HF exposure was assessed by questionnaire and environmental measurement. To measure finger nail F amount, Taves’ microdiffusion method using hexamethyldisiloxane modified by Whitford was applied. For grading acute F exposure level, we applied Acute Exposure Guideline level (AEGL) for 1 hour. F exposure was estimated from the difference of F mg/kg (⊿F) between the highest finger nail F concentration among the period of 3.0, 3.5, 4.0 months and the lowest concentration of baseline or 2.5 month. We estimated the increase ratio of finger nail F concentration due to 1mg of F ingestion according to the data of Whitford and Buzalaf.

RESULTS: Total 504 persons were included in grading F exposure level. Intraclass correlation coefficient for test-retest of finger nail F analysis ranged 0.67-0.98. The ⊿F accordant to upper limit of AEGL1, AEGL2, and AEGL3 were 3.83, 92.00, 168.67mg/kg, respectively. The exposure levels of participants were graded as following; 161 (31.9%) as non-exposure group (⊿F≤0), 270 (53.6%) as mild exposure group (0<⊿F≤3.83), 71 (14.1%) as moderate exposure group (3.83<⊿F≤92.00=AEGL1), and 2 (0.4%) as high exposure group (⊿F >92.00=AEGL2). NFEC was associated with environmental F exposure classification (PFEC) by plant death due to accidental exposure of HF (Spearman correlation test, r=0.138, p=0.002).

CONCLUSIONS:

Finger nail F could be a valid biomarker to evaluate the biological exposure of HF. The guidelines of NFEC were non-exposure (⊿F≤0), mild exposure (0<⊿F≤3.83), moderate exposure (3.83<⊿F≤92.00), and high exposure (⊿F >92.00).