Food safety implications of metals from bullet fragments in game meat: an investigation of bullet composition, bullet fragmentation and gastrointestinal solubility

Awareness of food safety in game meat is increasing, as it represents an important food source for certain population groups in Europe and is increasingly perceived by the general public as a sustainable and healthy alternative to conventional meat. Ensuring the safety of game meat presents several challenges that are less controllable than those in livestock meat production, due to the unique nature of hunting and processing. While (micro)biological safety remains the primary focus, the concern about contamination from hunting bullet fragments – particularly from lead-based rifle bullets – is increasingly gaining attention in food toxicology and environmental assessments. Despite the extensive data on the toxicity of lead (Pb), game meat represents one of the last uncontrolled sources of Pb exposure for humans. Conflicts of interest among different hunting stakeholders slow the implementation of legal measures to restrict the use of Pb in rifle bullets. While regulatory measures have predominantly focused on the ecological impacts of Pb-based ammunition, the aspect of food safety has received less attention, and comprehensive data are still limited. Copper-based alternative bullets have been developed with the aim of minimizing Pb exposure, yet their potential implications for food safety and human health are the subject of current investigation. This thesis aimed to systematically investigate the food safety implications of the use of Pb-based and alternative hunting rifle bullets through a multi-stage approach across primary production, meat processing, and game meat at the consumer level. Commercially available Pb-based and alternative hunting bullets of various designs were analyzed using energy-dispersive X-ray spectroscopy (EDX). The Pb-based bullets were primarily composed of lead (Pb), alloyed with antimony (Sb), and coated with copper-zinc (Cu-Zn) alloys, sometimes additionally coated with a nickel (Ni)-based layer. Due to the presence of metals with high toxic potential – particularly Pb, Sb, and the potentially concerning Ni – they were considered critical from a general food safety perspective. Alternative bullets consisted predominantly monolithic Cu-Zn alloys with an overall lower hazard potential. However, some variants contained aluminum (Al) in the alloy or bullet tip, Ni in coatings, and Pb as a component of the alloy – which may increase the hazard potential of these bullets. In addition, the fragmentation behavior of a typical deforming Pb-based hunting bullet was analyzed in roe deer using computed tomography (CT) to characterize the spatial distribution, number, and size of the fragments from the carcass to the edible parts during meat processing. The four examined roe deer contained numerous fragments, primarily concentrated near the wound channel. However, individual fragments were dispersed throughout the body, and a significant portion of the bullet mass was retained within the tissue. Many fragments were smaller than 1 mm³, with the smallest fragments detectable by CT measuring approximately 0.01 mm³. Due to the limited resolution of the CT scans, potentially smaller fragments may have remained undetected. During meat processing, the majority of detected fragments were removed, but individual fragments remained in edible tissues, including ribs, haunch, and shoulder. Additionally, a significant portion of the bullet mass was identified as a potential source of environmental contamination, represented by exiting bullet residues and fragments deposited in the viscera of the roe deer, which are commonly left in the forest. A semi-dynamic in vitro digestion model was employed to estimate the bioaccessibility of bullet fragments in meat under modeled conditions. For this purpose, beef samples were spiked with Pb and Cu particles of two different size fractions and subjected to a simulated digestion using artificial fluids. Metal concentrations in digestion fluids were quantified using inductively coupled plasma mass spectrometry (ICP-MS). While the applied conditions limited a direct interpretation of gastrointestinal solubility as bioaccessibility, the study offered preliminary insights into the dissolution behavior of metal particles in digestive fluids. Results showed that smaller particles exhibited higher solubility than larger particles for both elements. Moreover, Pb demonstrated greater solubility than Cu, with a substantial portion of Pb dissolving during the gastric phase. In summary, the findings of this study indicate that bullets have so far not been adequately considered as part of the game meat chain, and associated food safety aspects have only been addressed to a limited extent. Concerns may arise from the materials used in bullet construction, with Pb being of particular concern in Pb-based projectiles. However, alternative projectiles cannot be considered inherently safe, as they may also contain potentially concerning elements such as Ni, Al, or Pb. In practice, Pb-based bullets are highly prone to fragmentation, and the complete removal of fragments during meat processing cannot be guaranteed, potentially leaving residues in meat intended for human consumption. Small fragments are particularly difficult to remove, as their detection remains challenging even with technical equipment. In game meat, bullet fragments can pose both chemical and physical hazards to humans, as well as to wildlife when introduced into the environment and to pets when used as pet food. In the human gastrointestinal tract, Pb from these fragments may dissolve, potentially releasing concerning amounts of metal, which would be expected to cause adverse effects on human health. In contrast, even when present in high concentrations and small sizes, the dissolution of small fragments from Cu-based bullets would not be expected to exceed recommended daily Cu intake levels.