Human Visual Function in the North Carolina Clinical Studyon Possible Estuary-Associated Syndrome

Abstract

The U.S. Environmental Protection Agency assisted the North Carolina Department of Health and Human Services in conducting a study to investigate the potential for an association between fish kills in the North Carolina estuary system and the risk for persistent health effects. Impetus for the study was recent evidence suggesting that estuarine dinoflagellates, including members of the toxic Pfiesteria complex (TPC), P. piscicida and P. schumwayae, may release a toxin(s) that kills fish and adversely affects human health. This report describes one component of the study in which visual system function was assessed. Participants working primarily in estuaries inhabited by TPC or in off-shore waters thought not to contain TPC were studied. The potentially exposed estuary (n = 22) and unexposed offshore (n = 20) workers were matched for age, gender, and education. Visual acuity did not differ significantly between the cohorts, but visual contrast sensitivity (VCS), an indicator of visual pattern-detection ability for stimuli of various sizes, was significantly reduced by about 30% in the estuary relative to the offshore cohort. A further analysis that excluded participants having a history possibly predictive of neuropsychological impairment showed a similar VCS reduction. Additional analyses indicated that differences between the cohorts in age, education, smoking, alcohol consumption, and total time spent on any water did not account for the difference in VCS. Exploratory analyses suggested a possible association between the magnitude of VCS reduction and hours spent in contact with a fish kill. The profile of VCS deficit across stimulus sizes resembled that seen in organic solvent-exposed workers, but an assessment of occupational solvent, and other neurotoxicant, exposures did not indicate differences between the cohorts. These results suggest that factor(s) associated with the North Carolina estuaries, including the possibility of exposure to TPC toxin(s), may impair visual system function.

Apartment residents' and day care workers' exposures to tetrachloroethylene and deficits in visual contrast sensitivity.

“…The VCS deficits spanned the spatial frequency spectrum in both exposed groups, similar to the VCS deficit profiles seen in other solvent exposed populations (21)(22)(23)(24)(25)(26) and in contrast to the VCS spatial-frequency profiles observed in populations exposed to methyl mercury (44,45) and inorganic mercury (46,47). Differences between the shapes of altered VCS spatial-frequency profiles can indicate differential effects of various toxic exposures (40)(41)(42)(43)(44)(45)(46)(47)(48).…”

“…The possible trend toward worse color discrimination seen in the residential study, but not in the day care investigation, may have been caused by chance or a higher lifetime perc exposure (based on study mean perc concentration; Table 2) in the residential study (3,400 µg/m 3 years) than in the day care investigation (1,978 µg/m 3 years). In either case, the current results suggested that VCS may surpass color discrimination in sensitivity, perhaps caused by higher variability in color discrimination scores from control populations (99) than in VCS scores (40,(42)(43)(44)(45)(46)(47)(48).…”

“…VCS was significantly lower in the exposed groups than matched-control groups in both the residential study and day care investigation. The VCS deficits were likely of neurologic origin because the exposed and control groups did not differ in visual acuity, indicating that the groups did not different in optical refraction or in the ability to focus images on the retina (40,48). The VCS deficits spanned the spatial frequency spectrum in both exposed groups, similar to the VCS deficit profiles seen in other solvent exposed populations (21)(22)(23)(24)(25)(26) and in contrast to the VCS spatial-frequency profiles observed in populations exposed to methyl mercury (44,45) and inorganic mercury (46,47).…”

“…Persistent or permanent VCS deficits in the presence of normal visual acuity have been observed in workers exposed to styrene (21,22) and mixed solvents (23)(24)(25)(26), as have color discrimination deficits (27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38) in the absence of detectable optical, retinal, or optic nerve head pathology (39). VCS, a nonspecific indicator of subclinical visual impairment (40), also revealed neurologic effects associated with exposure to toxic Pfiesteria sp.-inhabited estuaries (40)(41)(42), with lead and mercury exposure (43)(44)(45)(46)(47), and was useful in differentiating vision effects from other exposure-induced deficits in neurobehavioral functions (48).…”

Possible estuary-associated syndrome: symptoms, vision, and treatment.

“…Recent evidence has suggested that the estuarine dinoflagellates Pfiesteria piscicida and P. shumwayae not only kill fish (8-10) on the Eastern Seaboard from Delaware to Florida (11) but also may pose a human health risk in laboratory (12) and natural settings (13)(14)(15). Humans who were exposed to estuaries of the Chesapeake Bay, Maryland, around the time of fish kills in 1997 had severe exposure-and duration-related reductions in neuropsychologic tests of cognitive and motor functions relative to unexposed, matched-control study participants (14).…”