Acute and subacute inhalation toxicities of phosphine, phenylphosphine and triphenylphosphine

Trivalent Phosphorus and Phosphines as Components of Biochemistry in Anoxic Environments

Phosphorus is an essential element for all life on Earth, yet trivalent phosphorus (e.g., in phosphines) appears to be almost completely absent from biology. Instead phosphorus is utilized by life almost exclusively as phosphate, apart from a small contingent of other pentavalent phosphorus compounds containing structurally similar chemical groups. In this work, we address four previously stated arguments as to why life does not explore trivalent phosphorus: (1) precedent (lack of confirmed instances of trivalent phosphorus in biochemicals suggests that life does not have the means to exploit this chemistry), (2) thermodynamic limitations (synthesizing trivalent phosphorus compounds is too energetically costly), (3) stability (phosphines are too reactive and readily oxidize in an oxygen (O₂)-rich atmosphere), and (4) toxicity (the trivalent phosphorus compounds are broadly toxic). We argue that the first two of these arguments are invalid, and the third and fourth arguments only apply to the O₂-rich environment of modern Earth. Specifically, both the reactivity and toxicity of phosphines are specific to aerobic life and strictly dependent on O₂-rich environment. We postulate that anaerobic life persisting in anoxic (O₂-free) environments may exploit trivalent phosphorus chemistry much more extensively. We review the production of trivalent phosphorus compounds by anaerobic organisms, including phosphine gas and an alkyl phosphine, phospholane. We suggest that the failure to find more such compounds in modern terrestrial life may be a result of the strong bias of the search for natural products toward aerobic organisms. We postulate that a more thorough identification of metabolites of the anaerobic biosphere could reveal many more trivalent phosphorus compounds. We conclude with a discussion of the implications of our work for the origin and early evolution of life, and suggest that trivalent phosphorus compounds could be valuable markers for both extraterrestrial life and the Shadow Biosphere on Earth.

The physiology and toxicology of acute inhalation phosphine poisoning in conscious male rats

Phosphine (PH₃) is a toxidrome-spanning chemical that is widely used as an insecticide and rodenticide. Exposure to PH₃ causes a host of target organ and systemic effects, including oxidative stress, cardiopulmonary toxicity, seizure-like activity and overall metabolic disturbance. A custom dynamic inhalation gas exposure system was designed for the whole-body exposure of conscious male Sprague-Dawley rats (250-350 g) to PH₃. An integrated plethysmography system was used to collect respiratory parameters in real-time before, during and after PH₃ exposure. At several time points post-exposure, rats were euthanized, and various organs were removed and analyzed to assess organ and systemic effects. The 24 h post-exposure LCt₅₀, determined by probit analysis, was 23,270 ppm × min (32,345 mg × min/m³). PH₃ exposure affects both pulmonary and cardiac function. Unlike typical pulmonary toxicants, PH₃ induced net increases in respiration during exposure. Gross observations of the heart and lungs of exposed rats suggested pulmonary and cardiac tissue damage, but histopathological examination showed little to no observable pathologic changes in those organs. Gene expression studies indicated alterations in inflammatory processes, metabolic function and cell signaling, with particular focus in cardiac tissue. Transmission electron microscopy examination of cardiac tissue revealed ultrastructural damage to both tissue and mitochondria. Altogether, these data reveal that in untreated, un-anesthetized rats, PH₃ inhalation induces acute cardiorespiratory toxicity and injury, leading to death and that it is characterized by a steep dose-response curve. Continued use of our interdisciplinary approach will permit more effective identification of therapeutic windows and development of rational medical countermeasures and countermeasure strategies.

Epidemiology of hydrogen phosphide exposures in humans reported to the poison center in Mainz, Germany, 1983-2003

BACKGROUND

Poisonings with rodenticides containing hydrogen phosphide-releasing compounds may lead to deleterious organ dysfunction and death. Since data of hydrogen phosphide poisonings is limited to case reports/series, this study was intended to elucidate hydrogen phosphide poisonings based on a 20-year data collection.

METHODS

Explorative data analysis of the Poison Center Mainz database looking for route of exposure, symptoms, and severity using the Poisoning Severity Score.

RESULTS

From 1983-2003, 188 hydrogen phosphide poisonings were reported. Sixty-five percent of these were unintentional residential, 28% attempts to commit suicide (intentional), 5% occupational, and 2% undetermined. In the majority of intentional poisonings the poison was ingested, whereas in unintentional poisoning of adults inhalation exposure dominated, caused by inappropriate self-protection from the released hydrogen phosphide gas during usage. Frequently observed symptoms in unintentional poisonings were nausea, vomiting, pain, coughing, and dizziness with no further worsening of symptoms. In intentional poisonings frequent symptoms were vomiting, somnolence, seizures, coma, and shock with two initially fatal poisonings. Follow-up on these cases showed a significant worsening of symptoms and a two-fold increase in fatal poisonings.

CONCLUSION

Route of exposure, severity of symptoms, and the necessary treatment differs substantially between unintentional and intentional poisonings. In this study, two initially symptomatic intentional poisonings were later reported fatal. Careful monitoring is recommended in symptomatic intentional poisonings.

Worker exposure standard for phosphine gas

The 1998 U.S. Environmental Protection Agency Office of Pesticide Programs (OPP) re-registration eligibility decision (RED) for phosphine fumigants has generated much interest in defining safe levels of exposure for workers and worker bystanders. This report summarizes the pertinent literature on phosphine toxicity, including animal inhalation studies and human epidemiology studies, and also describes a margin-of-exposure (MOE) analysis based on available worker exposure data. In addition, a safe occupational exposure limit is estimated using typical OPP assumptions, after determination of appropriate uncertainty factors, based on quality of data in the principal study and pharmacokinetic considerations. While a conservative 8-hour time-weighted average (TWA) of 0.1 ppm was calculated, the overall weight of evidence, from a risk-management perspective, supports a conclusion that an occupational TWA of 0.3 ppm provides adequate health protection. In addition, a 15-minute short-term exposure limit (STEL) of 3 ppm was estimated. Finally, in contrast to the MOE analysis described in the OPP's phosphine RED, the MOE analysis described herein does not indicate that fumigation workers are currently being exposed to unacceptable levels of phosphine. Collectively, these findings support the occupational exposure limits of 0.3 ppm (8-hour TWA) and 1 ppm (STEL) established in the updated applicator's manuals for phosphine-generating products, which recently received approval from OPP.

The Humaneness of Rodent Pest Control

Rat and mouse control methods potentially affect the welfare of many millions of animals every year. Here, the humaneness of the methods used in the UK and the USA is assessed in terms of their speed and mode of action, the appearance and behaviour of affected animals, experiences of human victims, long-term effects on animals that survive exposure, and welfare risks to non-target animals. Several methods emerge as relatively humane: cyanide, alpha-chloralose, electrocution traps and well-designed snap traps all usually kill swiftly and with little distress. Preventative methods such as rodent-proofing are also humane, as well as an essential — and probably under-used — component of effective control. However, anticoagulant poisons, the most common means of controlling rodents, generally take several days to kill, during which time they cause distress, disability and/or pain. Sub-lethally affected animals are also likely to experience haemorrhages and their sequelae, and carnivores feeding on affected rodents may be secondarily poisoned. The acute rodenticides zinc phosphide and calciferol are also generally inhumane, the former typically causing severe pain for several hours, and the latter, pain and illness for several days. Sticky boards, to which rodents become adhered by the feet and fur until they are killed or simply eventually die, also raise very serious welfare concerns. This evidence highlights remarkable paradoxes in the way society treats different classes of animal, and argues for more education, legislation and research targeted at reducing the vast numbers of rodents currently killed inhumanely.

Determination of genotoxic and other effects in mice following short term repeated-dose and subchronic inhalation exposure to phosphine

Phosphine is an important fumigant in the grain industry and has been reported to be genotoxic in occupationally exposed fumigators. This study reports on the effects of phosphine inhalation exposure at up to, and exceeding, occupational relevant levels in a subchronic (0.3, 1.0 and 4.5 ppm, 13 weeks) and a short term repeated-dose (5.5 ppm, 2 weeks) study in both sexes of Balb-c mice. The following end-points were examined: micronucleus induction in bone marrow, peripheral blood, spleen lymphocytes and skin keratinocytes, mutations at the hypoxanthine-guanine phosphoribosyl transferase locus in lymphocytes, and weight gain and relative organ weights (kidneys, lungs, liver, heart, brain and spleen). After subchronic exposure, there was a highly significant negative linear correlation between proportional weight gain and exposure in both sexes (multiple linear regression, r = -0.56, P < 0.0001), with female mice showing a greater effect. Females also showed an increase in relative organ weights at the highest test dose, in contrast to males where there was a slight decrease. A statistically significant increase in micronucleus frequency was seen in the bone marrow and spleen lymphocytes of both sexes, but only at the highest concentration. The short term repeated-dose study revealed a slight decrease in weight gain in both sexes, with a greater effect in females. It is concluded that phosphine is weakly genotoxic in both sexes of mice, and has an effect on weight gain. However, the weak genotoxic effect may not be biologically significant as it was seen only in the subchronic study and only at the highest test concentration of 4.5 +/- 0.8 ppm (approaching the LD50). Although such exposure conditions are unlikely to be encountered in an occupational environment, caution should continue to be exercised in the use of phosphine until more data become available.