Effects of Lifetime Lead Exposure in Monkeys on Detection of Pure Tones

Abstract

Increased detection thresholds for pure tones were observed in a large cohort of children exposed to lead environmentally while smaller studies in lead-exposed workers have reported conflicting results on assessments of auditory function. Pure tone detection thresholds were determined in a group of monkeys (Macaco fascicularis) dosed with 2 mg/kg/day of lead from birth through testing at 13 years of age. Blood lead concentrations were stable at about 30 /ig/dl until monkeys were 10-11 years of age, at which time they increased to between 50 and 170 /xg/dl. Five age-and rearingmatched monkeys served as controls. Detection thresholds were determined at six frequencies between 0.125 and 31.5 kHz. Earphones were fit over both ears, and thresholds were determined for each ear separately. The monkey signaled detection of the tone by breaking contact with a stainless steel bar. Three lead-exposed monkeys exhibited normal pure tone detection functions. Three monkeys had thresholds outside of the control range at some frequencies; there was a tendency for higher frequencies to be differentially more affected. These findings are consistent with reports of elevated pure tone thresholds in humans exposed to lead developmentally, although the effect is smaller than might have been predicted given the concurrent blood lead concentrations of these monkeys.» 1997 Sod«y of Toxicology.

Hearing Loss and Heavy Metal Toxicity in a Nicaraguan Mining Community: Audiological Results and Case Reports

“…In this same study, prolonged latencies of ABR waveforms were also seen in those children with the highest lead levels [Osman et al, 1999]. A report on chronically lead-exposed monkeys also revealed elevated PTTs in roughly half of exposed animals compared to control animals [Rice, 1997]. Furthermore, DPOAE responses in these monkeys revealed significantly reduced emissions in 20% of exposed animals [Lasky et al, 1995].…”

Emissões otoacústicas - produto de distorção em indivíduos expostos ao chumbo e ao ruído

“…Essa constatação foi apresentada por Rice 16 em seus estudos com cobaias, nos quais observou que os limiares elevados apresentaram padrões desordenados de respostas, bem diferentes daqueles encontrados nas patologias cocleares causadas por agentes que danificam as células ciliadas externas do Órgão de Corti.…”

Early lead exposure effects on an auditory threshold task in the rhesus monkey (Macaca mulatta)

“…For example, among the 6-19 year olds evaluated in the Hispanic Health and Nutrition Examination Survey, an increase in blood lead level from 7 to 18 mg/dl was associated with approximately a 2 dB hearing loss at all frequencies tested (500, 1,000, 2,000, 4,000 Hz) in children (Schwartz & Otto, 1991, p. 303). Elevated thresholds for pure tones, particularly at higher frequencies, were also reported for a group of 13-year-old monkeys (M. fascicularis) that had been exposed to lead daily since birth (Rice, 1997).…”

“…The contribution to these effects of current versus previous blood lead level could not be addressed directly in these studies, but was addressed indirectly by Robinson et al Results suggested the effects were due primarily to current blood lead levels. Elevated thresholds for pure tones, particularly at higher frequencies, were also reported among a group of 13-year-old lead-exposed monkeys (Macaca fascicularis) (Rice, 1997). However, exposure for those monkeys was continuous from birth to the time of testing.…”