PARAQUAT, a bypyridyl herbicide, is used widely throughout the world. Its development was considered to be a major advance in herbicide safety because the chemical decomposed rapidly into harmless compounds when it contacted soil and left no toxic residue. Despite its theoretical safety, however, poisonings have been described virtuFulminant Paraquat poisoning occurs following ingestion of more than 15 ml of a 20% solution. Victims who survive the severe neurologic, renal, and hepatic complications that occur during the first hours to days following ingestion often die several weeks later from profound pulmonary fibrosis. Persons may also suffer from ulceration of the oropharynx and esophagus. Death can occur as soon as 24 h and as long as 3 wk after Paraquat ingestion. Moderate to severe Paraquat poisoning results from the ingestion of 20 to 40 mg/kg body weight or, for the average adult, less than 15 ml of a 20% solution. Survivors of even this smaller dose can develop fatal pulmonary disease.
The mechanism of Paraquat poisoning is related to its function as a redox agent and the production of oxygen free radicals. Paraquat reduction is coupled with the reduction of molecular oxygen, which results in the production of highly toxic superoxide anion, single oxygen and possibly hydroxyl radicals. Experimental antioxidant therapies with vitamins E and C have been tried, but they have not been shown to alter the final outcome.[2-4]ally everywhere Paraquat has been used
The prevalence of Paraquat poisoning is difficult to assess because of the lack of morbidity and mortality data from countries where the herbicide is used routinely. The World Health Organization (WHO) does not maintain separate statistics for Paraquat poisonings; rather, it groups agricultural chemical poisonings together. A review of the reported incidence of Paraquat poisoning shows high rates in Fiji and Japan (47.0 and 11.0 deaths per million population per year, respectively). Much lower rates are seen in Ireland (2.7 per million population per year), Great Britain (0.66 per million population per year), and the United States (0.004 per million population per year).' To date, only one clinical report of Paraquat ingestion has appeared from Latin America, although Paraquat is among the best known and most commonly used agrochemicals.
In 1989, several cases of Paraquat ingestion at the Hospital General "J" in Comitan and the Comitan Health Research Center prompted investigation of herbicide poisoning and the circumstances surrounding toxic ingestions. We report in this article the first case series of Paraquat poisonings from Latin America and describe risk factors for Paraquat ingestion.
Materials and methods
The study area included the municipalities of Comitan, Trinitaria, Amatenango, Margaritas, Comalapa, and Chicomuselo in Chiapas, Mexico (population 315 00; Fig. 1). Cases of Paraquat ingestion were identified through a review of all hospital inpatient records at Comitan Regional Hospital, the principal referral hospital in the region, between January 1988 and April 1990. Mortality data from the 1989 civil registries were also reviewed; these registries are incomplete sources of mortality data, especially from rural communities. Cases were also solicited from rural health promoters.
A case was defined as either a person with a clinical illness consistent with Paraquat ingestion who was identified as having ingested Paraquat or as a registry death in which Paraquat was identified as the cause of death.
Age, sex, residence, and clinical outcome were recorded for all cases. Clinical course of illness and treatment were documented inconsistently and were, therefore, not analyzed. A detailed questionnaire was administered to survivors or household relatives of nonsurvivors. The questionnaire addressed issues of socioeconomic status and agricultural exposure of the victim. Other questions included location of purchase of the herbicide, the victim's knowledge of its use, and storage methods of the herbicide in or about the victim's home. Information about suicidal intent and coincident alcohol intoxication in the victim was also elicited.
Twenty-five cases of Paraquat ingestion were identified; of these, 16 died and 9 survived. Twenty 60%) of the cases were men. There were 16 cases for whom questionnaire information was available (interview cases); sex and age of interview cases were similar to those of noninterview cases. Eleven of the 12 male interview cases were agricultural workers, and I described himself as a day laborer. The 4 female interview cases were described as housewives who were married to agricultural workers. All interview cases were literate.
Eleven of the 16 interview cases lived in one-room houses. Approximately one-half of those interviewed reported that the herbicide was stored in the "patio" of the house; the remaining one-half indicated that Paraquat was either kept inside the house or they were unable to recall where the herbicide was stored. Three interview cases kept the herbicide under the bed. None kept Paraquat in its original container, and several kept the chemical in soft drink containers. Eight (50%) of the interview cases bought Paraquat at a store that specialized in selling agrochemicals, but 14 (87%) of the interview cases stated that instruction for its use came from a friend; none had learned from a professional. Only 4 (25%) interview cases knew the proper dilution for use of the commercial preparation.
In 9 (56%) of the 16 interview cases, suicide was the motive for Paraquat ingestion; 7 (78%) of these cases died. Two additional interview cases were described as being chronically depressed, but suicidal intent was uncertain. Nine (56%) of the interview cases were described as intoxicated with alcohol at the time of the ingestion; 5 of these also had suicidal ideation. Only 1 case was totally accidental, i.e., neither suicidal intent nor alcohol ingestion. This case had siphoned the herbicide when he mistook it for diesel fuel. Most (56%) of the interview cases were alone at the time of the ingestion; 31% were in the company of another person; 2 (13%) interview cases did not provide this information.
This is the first series of Paraquat poisonings reported from Latin America. Southern Chiapas now ranks among those regions of the world with the highest known mortality rates from Paraquat ingestion. if no other cases occurred in the region during the period of study, the mortality rate from Paraquat would exceed 20 per million population per year. It is our impression, however, that the 25 cases described here represent only a fraction of the Paraquat intoxications in southern Chiapas. Episodes that occurred in remote rural communities, where access to hospital care is minimal, were likely to have been unrecognized.
The case-fatality rate from Paraquat ingestion in Chiapas is similar to that reported in other parts of the world.[6-8] Deaths are a function almost exclusively of the amount of Paraquat ingested, and therapy of any kind has very little if any effect on the final outcome.[3,4,9] Because of the retrospective nature of this study, the amount of Paraquat ingested by the subjects could not be ascertained.
As has been seen in studies from other regions, the intent to commit suicide was the most commonly expressed motive for Paraquat ingestion.[8, 10-12] in more than half of the attempted or successful suicides, the patients were also intoxicated with alcohol. The herbicide, which was often stored in an unlabeled bottle within the household, provided a convenient method for impulsive, suicidal behavior. Unfortunately, the outcome of even a small, gestural ingestion is often fatal. Once a lethal dose is taken, the inevitable, grim outcome cannot be countered.
Intervention to prevent poisoning should be directed toward prevention of impulsive action. For example, Paraquat could be distributed in "child-proof" containers, making it difficult for an inebriated adult to open. in addition, the concentration of marketed solution could be lowered so that a lethal dose would require a larger volume. Paraquat could also be sold in a solid, rather than liquid, form. A substance that is foul smelling or has to be mixed with water to be ingested might be less attractive for an impulsive action, although such alterations in formulation of the chemical in Japan have not reduced the number of Paraquat-related deaths. in Mexico, Paraquat is sold as a 20% solution that is diluted and sprayed from plastic, back-pack tanks. By law, vendors must be certified to sell Paraquat, and all injuries must be reported.13 Agricultural extension experts are available in the communities to explain the use of herbicides. Yet, this study found that victims of poisoning did not know the proper dilution for Paraquat use; they learned to use Paraquat from friends, rather than from qualified authorities, and they stored the chemical in a suboptimal manner. Although these victims of poisoning may not represent the population of Paraquat users in the state, it seems likely that educational efforts directed at populations at risk would enhance understanding of the toxicity of this agent and foster improved management of hazardous agrochemicals. Some might claim, however, that only banning the chemical can reduce the rates of fatal ingestion of this highly lethal agent.