Exposure to lead-free frangible firing emissions containing copper and ultrafine particulates leads to increased oxidative stress in firing range instructors

Abstract

Background: Since the introduction of copper based, lead-free frangible (LFF) ammunition to Air Force small arms firing ranges, instructors have reported symptoms including chest tightness, respiratory irritation, and metallic taste. These symptoms have been reported despite measurements determining that instructor exposure does not exceed established occupational exposure limits (OELs). The disconnect between reported symptoms and exposure limits may be due to a limited understanding of LFF firing byproducts and subsequent health effects. A comprehensive characterization of exposure to instructors was completed, including ventilation system evaluation, personal monitoring, symptom tracking, and biomarker analysis, at both a partially enclosed and fully enclosed range.

Results: Instructors reported symptoms more frequently after M4 rifle classes compared to classes firing only the M9 pistol. Ventilation measurements demonstrated that airflow velocities at the firing line were highly variable and often outside established standards at both ranges. Personal breathing zone air monitoring showed exposure to carbon monoxide, ultrafine particulate, and metals. In general, exposure to instructors was higher at the partially enclosed range compared to the fully enclosed range. Copper measured in the breathing zone of instructors, on rare occasions, approached OELs for copper fume (0.1 mg/m³). Peak carbon monoxide concentrations were 4-5 times higher at the partially enclosed range compared to the enclosed range and occasionally exceeded the ceiling limit (125 ppm). Biological monitoring showed that lung function was maintained in instructors despite respiratory symptoms. However, urinary oxidative stress biomarkers and urinary copper measurements were increased in instructors compared to control groups.

Conclusions: Consistent with prior work, this study demonstrates that symptoms still occurred despite exposures below OELs. Routine monitoring of symptoms, urinary metals, and oxidative stress biomarkers can help identify instructors who are particularly affected by exposures. These results can assist in guiding protective measures to reduce exposure and protect instructor health. Further, a longitudinal study is needed to determine the long-term health consequences of LFF firing emissions exposure.

Keywords: Biomarkers; Carbon monoxide; Copper; Exposure assessment; Firing range; Oxidative stress; Ultrafine particulate; Ventilation.

Fig. 1

Schematics of small arms ranges at WPAFB and JBC. A Illustration of the fully enclosed range design at WPAFB where ventilation is supplied by a radial plenum. B Illustration of the partially enclosed range design at JBC where ventilation is provided by banks of industrial fans

Fig. 2

Air flow velocities and direction at firing line for classes at WPAFB and JBC. A Air velocity measured over three days at WPAFB for the indicated class types. B Air velocity measured at JBC for the indicated class types. C Directional air flow velocities measured at WPAFB. D Directional air flow velocities measured at JBC. Measurements were made at each base prior to or after each of the M9. M4, and M4/M9 classes

Fig. 3

Copper exposure measured in the breathing zone of instructors. A Average 8 h TWA Cu measurements at both WPAFB and JBC based on class type. Not including canceled M4 class. Error bars represent SEM. *p < 0.01. #p < 0.01 versus WPAFB. n shown above x-axis. B Total copper measurements collected at WPAFB. C Cu measured in the respirable range at WPAFB. D Total Cu measurements collected at JBC. E Cu measured in the respirable range at JBC. Error bars represent SEM. “Small Class” represents a class size of less than 5 students and contains data from both M4 and M9 refire events. 8 rds = 8 rounds of ammunition fired. “Clean” indicates a day with no class at JBC in which range instructors were cleaning the range

Fig. 4

CO and particle exposure based on class type. A Average instructor CO 8 h TWA by class type. B Peak CO 8 h TWA by class type. C Average instructor particle concentration LDSA 8 h TWA by class type D Peak LDSA by class type. Data are represented individual values along with bars representing the mean ± SEM. *p < 0.05 JBC versus all WPAFB. #p < 0.05 v JBC M4/M9. ^p < 0.05 v WPAFB M9. §p < 0.05 versus WPAFB M4

Fig. 5

Representative time series plots for average particle concentration. Data are presented as average particle concentration for all of the instructors on the line during the M4/M9 combined classes on 15 MAR 19 at WPAFB and 10 JUL 19 at JBC. A WPAFB M4; B WPAFB M9; C JBC M4; D JBC M9. Red numbers above peaks represent the number of rounds fired by each shooter in the class. Nine shooters were present at WPAFB and seventeen at JBC. Blue stars represent times where firing was paused due to grading, instruction, or moving barricades

Fig. 6

Positive correlations between 8 h TWA CO, Cu, and LDSA. A Correlation between 8 h TWA CO and LDSA, R² = 0.836, p < 0.0001. B Correlation between 8 h TWA CO and Cu, R² = 0.834, p < 0.0001. C Correlation between 8 h TWA Cu and LDSA, R² = 0.989, p < 0.0001

Fig. 7

Lung function measured by spirometry. Spirometry tests were administered pre- and post- shift for both control participants and instructors on the line at both WPAFB and JBC. A FVC, B FEV1. Data are represented as individual points with the bars representing mean ± SEM

Fig. 8

Urinary 8-OHdG levels. A WPAFB; B JBC; C WPAFB and JBC combined. *p < 0.05 v control. Data are represented as individual points with the bars representing mean ± SEM

Fig. 9

Urinary metal analysis. A WPAFB; B JBC. *p < 0.05 versus control post. Cu was normalized to urinary creatinine

Fig. 10

Simultaneous plots of air monitoring data and 8-OHdG levels over time. A 8 h TWA CO and 8-OHdG levels for line instructors and controls at WPAFB. B 8 h TWA LDSA and 8-OHdG at WPAFB. C 8 h TWA Cu and 8-OHdG at WPAFB. D CO and 8-OHdG levels for line instructors at JBC. E LDSA and 8-OHdG levels for line instructors at WPAFB. F LDSA and 8-OHdG levels for line instructors on the line at JBC