Because of the delayed pulmonary toxicity, prompt immobilization of the paraquat to prevent absorption is important. Adsorbents (eg, activated charcoal, Fuller’s earth) are routinely given to bind the paraquat and minimize its absorption. Gastric lavage is not recommended as it may promote aspiration from the stomach into the lungs. Once the paraquat is absorbed, treatment is successful in less than 50% of cases. Monitoring of plasma and urine paraquat concentrations is useful for prognostic assessment. Computed tomography scanning has also been used to follow the pulmonary lesions as they develop and to help with prognosis. The pulmonary proliferative phase begins 1–2 weeks after paraquat ingestion. Although a few reports indicate some success with dialysis, hemodialysis and hemoperfusion rarely change the clinical course. Many approaches have been used to slow or stop the progressive pulmonary fibrosis. Immunosuppression using corticosteroids and cyclophosphamide is widely practiced, but evidence for efficacy is weak. Antioxidants such as acetylcysteine and salicylate might be beneficial through free radical-scavenging, anti-inflammatory, and nuclear factor kappa-B inhibitory actions. However, there are no published human trials. The case fatality rate is high in all centers despite large variations in treatment. Patients require prolonged observation and treatment for respiratory and renal insufficiency if they survive the acute stage of poisoning.
Highly halogenated biphenyl compounds, which have desirable properties for insulation, fire retardancy, and many other uses, were manufactured in large quantities during the mid-20th century. The quantities produced and the almost universal dispersion of the materials in which they were incorporated have produced an enormous environmental problem. Both chlorinated and brominated biphenyls are environmentally dangerous and significantly toxic, and are now banned from use.
The polychlorinated biphenyls (PCBs, coplanar biphenyls) were used as dielectric and heat transfer fluids, lubricating oils, plasticizers, wax extenders, and flame retardants. Their industrial use and manufacture in the USA were terminated by 1977. The chlorinated products used commercially were actually mixtures of PCB isomers and homologs containing 12–68% chlorine. These chemicals are very stable, highly lipophilic, poorly metabolized, and very resistant to environmental degradation; thus they bioaccumulate in food chains.
Food is the major source of PCB residues in humans. Accumulation of PCB in fish species led Canada and the USA to restrict commercial fishing and to limit consumption of fish from the Great Lakes of North America (see Box: Bioaccumulation & Biomagnification, earlier). In addition, large industrial site contamination, illegal dumping, migration from hazardous waste sites and other large-scale sources, and widespread use of PCBs in electrical transformers has led to multiple localized areas of contamination and human exposure. Leakage of transformer dielectric fluids in neighborhoods and backyards has caused significant numbers of serious but highly localized PCB exposure events.