Effects of lead shot ingestion on bone mineralization in a population of red-legged partridge (Alectoris rufa)
Introduction
Lead (Pb) poisoning by shot ingestion is a widespread problem affecting many wild bird species, especially those inhabiting areas of intense recreational hunting activities (Clark and Scheuhammer, 2003, Fisher et al., 2006, Franson and Pain, 2011). To implement alternative restorative/protective policies, it is important to evaluate first the availability of the Pb shot in the field and the direct impact of this contaminant on the health of bird populations. Knowledge about the type and concentration of contaminants in biological tissues (e.g., liver, kidney, bone) helps identifying cases of poisoning or exposure to contaminants in the environment (Jeng et al., 1997, Mateo et al., 1997, Van Eeden and Schoonbee, 1996, Wayland et al., 1999). Bone is a useful tissue to describe long-term exposure due to its slow turnover rate and because Pb preferentially accumulates in bone (Franson and Pain, 2011, Gangoso et al., 2009, Wayland et al., 1999). Bone constitutes a long-term repository for Pb, containing approximately 90% of the total body burden in birds and mammals (Ethier et al., 2007). This efficiency of bone to store Pb is due to the fact that Pb substitutes for calcium in apatite, which is the main mineral component of bone (Sukuki et al., 1981).
Bone is a mineralized tissue composed of an organic matrix, mainly collagen, and nano-sized hydroxylapatite crystals (Bonucci, 2012). Bone plays an essential role in many metabolic activities as a mineral reservoir that absorbs and releases ions needed for various cell functions (Lowenstam and Weiner, 1989). Several biological processes are involved in controlling bone tissue turnover and development. These processes can be altered by the state of health of the organism as well as other genetic and environmental factors (i.e., pollution). In fact, several toxicological studies have demonstrated how environmental pollutants may cause malformations and abnormal mineralization and composition of bone tissue (Berglund et al., 2000, Lind et al., 2004, Puzas et al., 1992). In particular, Pb may indirectly alter bone mineralization by provoking kidney dysfunction and thus altering vitamin D metabolism which is involved in calcium (Ca) homeostasis (Scheuhammer, 1987). Additionally, Pb toxicity can directly affect bone mineralization by altering osteoblast and osteoclast functions (Beier et al., 2013, Pounds et al., 1991, Puzas et al., 1992) and decreasing the activity of plasma alkaline phosphatase as observed in birds (Mateo et al., 2003). Furthermore, these alterations in bone mineral metabolism may induce bone osteoporosis and bone weakness, increasing the risk of fractures (Fleming et al., 2000, Gangoso et al., 2009) as described with other heavy metals (Larison et al., 2000).
Several analytical techniques are available to assess changes in bone composition (Boskey and Mendelsohn, 2005a, Hassenkam et al., 2004, Olszta et al., 2007, Peters et al., 2000). Fourier transform infrared (FTIR) spectroscopy is particularly useful as it provides detailed qualitative and quantitative information about the molecular constituents of bone (e.g., carbonate, collagen and phosphate: Boskey and Mendelsohn, 2005a, Gadaleta et al., 1996, Miller et al., 2001, Rey et al., 1991, Termine and Posner, 1966). In this sense, infrared spectroscopy has been used to identify abnormal mineral composition due to different pathological conditions affecting bone (Alvarez-Lloret et al., 2009, Boskey and Mendelsohn, 2005b, Rodriguez-Navarro et al., 2006). The use of FTIR allows a better and more detailed comprehension of changes in mineralized tissues associated with different bone disorders related with exposure to pollutants.
In this investigation, we have studied a population of red-legged partridge (Alectoris rufa) exposed to Pb contamination on farmland containing a high density of spent Pb-shotgun pellets from hunting activities (Ferrandis et al., 2008). Liver, femur, and muscle Pb levels were previously analyzed in red-legged partridges as an indicator of Pb exposure (Ferrandis et al., 2008, Mateo et al., 2011). Since bone metabolism is highly sensitive to Pb toxicity, we have undertaken this study to determine if Pb exposure has altered bone mineralization in this population of birds. For this purpose, we have employed a combination of analytical techniques including graphite furnace atomic absorption spectroscopy (GF-AAS), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses to fully characterize bone properties in these birds. The combined use of these techniques can provide detailed compositional and structural information of bone tissue and help us to define the health condition of bone in relation to Pb levels. Furthermore, bone condition can help us define which specific physiological processes, if any, may have been altered by Pb exposure. Finally, we provided explanations to the possible alteration on the bone mineralization processes induced by Pb exposition and its possible relationship with impaired bone strength and bone diseases.
Section snippets
Study area
The study was carried out on a ~ 3,500 ha private upland small-game hunting estate located in the south of La Mancha region, Albacete province, central-southeastern Spain. Red-legged partridge, the focal species of this study, is a common game bird species in South Western Europe, inhabiting croplands, orchards, open woodlands, and dry hilly land with scattered small bushes up to about 1,300 m in montainous foothills. The diet of the species consists of wild and cultivated grasses and forage
Results
Bone parameter measurements are reported as mean values with standard errors (1 sigma) and ranges (minimum and maximum limits) by sex and age in Table 1. Mean Pb concentration in femur was significantly higher in adults than in juveniles, 1.76 and 0.55 μg/g, respectively (F1, 34 = 19.08, p < 0.001; Fig. 1). Lead concentrations were also significantly higher in adults males and females (1.97 and 1.51 μg/g, respectively), than in juveniles (0.64 and 0.49 μg/g; Table 1). On the contrary, none of the
Discussion
Previous studies of this partridge population have demonstrated that birds were exposed to significant Pb levels (Ferrandis et al., 2008). Nevertheless, no notable effects on body condition, organ weight, or abdominal fat as health indicators were detected. The apparent lack of effect was attributed to the fact that the partridge, being a galliform species, may be more resistant to Pb toxicity than other more sensitive species (i.e., altricial birds; Scheuhammer, 1987). In the current study, we
Conclusions
In summary, we have investigated the effects of Pb exposure on bone mineralization in a wild population of red-legged partridges. Despite the difficulties of controlling for all the factors involved in Pb exposure in any wild population, some significant effects were observed in the bone mineral properties determined. Specifically, data obtained from FTIR spectroscopy and XRD analyses revealed a reduction in the degree of bone mineralization and an increase in the crystallinity of bone mineral
Conflicts of interest
The authors declare that there is not conflict of interest in this study.
Acknowledgements
We thank “Centro de Instrumentación Científica” (Universidad de Granada) and the staff for their technical support, and the owner of the farm, Alejandro Sánchez, for giving the partridges analyzed in the study. This work was supported by Research Projects of the Spanish government: CTM2007-65713, CGL2011-25906, GREIB.PYR-2010-01 and the Junta de Andalucía (research group RNM-179 and project P08-RNM-4169). Currently, MMH benefits from a Marie Curie Intra-European Fellowship for Career
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