Genetic engineering has raised the question of whether its products create unintended health effects for consumers, but how do conventionally bred products compare along the continuum of genetic modification? Celery provides an interesting case, as it contains naturally occurring toxic chemicals called psoralens, which are secondary metabolites found in a variety of fruits and vegetables, and members of the class of compounds called furanocoumarins (Diawara and Kulkosky, 2003). The psoralen in celery provides it with a biological defense mechanism of sorts—if it suffers disease or has been bruised, the celery plant can produce up to 100 times the level of psoralen that it typically contains, thus protecting itself from attacks by pests. The production of psoralens also depends on factors such as temperature, season and, particularly, availability of sunlight (Diawara et al., 1995). Psoralens temporarily sensitize human skin to longwave ultraviolet radiation. Consequently, they have been used for more than 25 years as a component in phototherapy—a means of treating acute skin diseases (New Zealand Dermatological Society, 2002).
However, psoralen in celery has been implicated in cases of skin irri-tation, such as dermatitis, among farm workers and other handlers of these plants, and studies have suggested a potential correlation between psoralens and cancer in laboratory mice (Beier, 1990). Moreover, celery cultivars produced using conventional breeding methods—intended to enhance insect-resistance and aesthetic appeal to consumers through increased production of psoralen—have been associated with cases of dermatitis among grocery workers, as well as further cases of photosensitivity among farm workers handling these plants (Ames and Gold, 1999). This form of dermatitis, or “photodermatitis,” has been observed as far back as 1961 in field workers who had handled celery infected with the disease pink rot (Birmingham et al., 1961). The Centers for Disease Control and Prevention reports cases dating back to 1984 of severe skin rashes among laborers who handled celery on a regular basis. The initial onset of these cases spawned a study by the National Institute for Occupational Safety and Health, in which there appeared to be a relationship between the handling of celery and prolonged exposure to sunlight. In the study that was undertaken in 1984, a number of grocery workers who handled celery on a regular basis also had used a tanning salon, suggesting to researchers that the ultraviolet light from tanning had exacerbated the reactions of the workers’ skin in response to the celery they had handled (CDC, 1985). Exposure to elevated levels of psoralens remains a problem for laborers such as field workers, as constant exposure to sunlight—combined with the handling of vegetables such as celery—can induce reactions such as those occurring in the skin. Psoralens continue to be regarded as naturally occurring toxicants (Beier, 1990).