The use of lead in ammunition for hunting exposes waterfowl to lead poisoning (plumbism) by accidental consumption of shotgun pellets. To test this hypothesis we sampled 18 liver tissue samples of Snow Goose (Chen caerulescens) collected during the 2012-2013 hunting season in a wetland near the city of Durango, Mexico. We quantified liver lead levels using an atomic absorption spectrophotometer and portions of liver were fixed and stained for their histological study. Average lead concentration (in dry weight) were under the normal range (mean = 0.73 ± 0.2, standard error) which do not represent any risk of poisoning. Liver tissue injuries were not observed in the histopathological analysis, suggesting no reaction to a xenobiotic agent such as lead. Gastrointestinal content analysis showed lead pellet in the gizzard of one individual, but we could not find a relationship between pellet ingestion and lead concentration in the liver. Although the results did not provide evidences of lethal or sublethal effects caused by lead poisoning, they show a possible risk due to the presence of lead pellets in the digestive tract.
Birds have been commonly used as valuable environmental indicators in eco-toxicological studies and are crucial to properly document the qualitative and quantitative environmental changes of certain environmental pollutants owing to both natural and anthropogenic causes [
In Mexico, there are not many wildlife studies about heavy metals and metalloids contents in waterfowl. Recent studies [
Among heavy metals, lead has a very special interest because of its use in the manufacture of ammunition for shotguns and the Mexican government does not apply any restrictions on its use. Unfortunately, hunting is a common activity in wetlands where many species of resident and migratory water birds live. Lead is a heavy metal that has no physiological significance and is highly toxic. The absorption of minimum concentrations produces various sublethal effects in birds and in high concentrations can cause death [
The objective of this study was to determine the concentration of lead in liver tissue of Snow Goose (Chen caerulescens) and relate it to lethal or sublethal effects on health.
We conducted this study in 96.0 ha of the UMA Ejido “El Arenal” (SEMARNAT-UMA-EX0336-DGO) Durango, Mexico (
The climate is BS1kw (w), semidry and semiarid [
Shrub vegetation is characterized by Opuntia leucotricha, O. streptacantha, O. megacantha, Acacia tortuosa, Prosopis juliflora, Mimosa biuncifera, O. imbricata, Yucca spp., and some Agave ssp. The herb stratum is dominated by grasses such as Bouteloa gracilis, B. curtipendula, B. hirsuta, Setaria macrostachya, Leptochloa dubia, Stipa eminens, Botriochloe barbinoidis, Aristida ternipes, A. glauca, A. divaricata, Heteropogon contortus and Melinis repens [
During the hunting season (December 2012 to March 2013) 18 snow geese were collected. Sampling depended on geese hunted during the season. Each goose was weighed on a TorRey scale (Model L-EQ 10/20) with a 10 kg capacity and 0.02 kg accuracy. At the same time livers were removed and weighed on an OHAUS balance (Model CS 2000) with a 2000 g capacity and 1 g accuracy.
The hepatosomatic index (HSI) was calculated as:
Livers were placed in sterile plastic bottles and stored in coolers and sent to the FMVZ laboratory and kept at a temperature of −20˚C (Friend and Franson [
A fraction (1 g) of the liver was sent to the laboratory of CIIDIR-Durango where the concentration of Pb was determined with an atomic absorption spectrophotometer (Perkin Elmer AAnalyst 700), in agreement to NOM- 010-ZOO-1994. Lead concentrations were obtained in both dry and wet weight, to facilitate comparison with values reported in other studies.
The histological analysis was performed by slicing a portion of each liver and fixing in 10% formalin to perform a microscopic examination. Samples were cut to 4 microns with a microtome and stained with a hematoxylin- eosin solution. This microscopic examination allowed us to observe the characteristics of cells and possible changes to support the diagnosis. We used a Leica ICC50HD microscope with an integrated digital photography system connected to a computer.
Statistical analysis of data was performed using the Number Cruncher Statistical Software (NCSS) 2000 program [
Mean lead concentration (wet weight) was 0.17 ppm ± 0.04 error standard (n = 18). Lead concentration in liver tissue (
Lead concentration (ppm) | ||||||
---|---|---|---|---|---|---|
Body weight (g) | Liver weight (g) | HSI | Dry weight | Wet weight | ||
Mean | 1867 | 29.27 | 1.57% | 0.73 | 0.17 | |
Median | 1900 | 28.30 | 1.46% | 0.39 | 0.11 | |
Standard error | 61.62 | 2.38 | 0.11% | 0.20 | 0.04 | |
Lower limit 95% | 1736 | 24.23 | 1.32% | 0.31 | 0.07 | |
Upper limit 95% | 1997 | 34.29 | 1.81% | 1.15 | 0.27 | |
liver of waterfowl express the likelihood of intoxication as 2 - 6 ppm subclinical intoxication, 6 - 15 ppm clinic intoxication, and over 15 ppm severe intoxication. The maximum acceptable lead levels in wildlife are based on experiments on wild birds with no previous exposure to lead, and with the administration of different doses of lead in which sublethal effects and death occurred. Waterfowl with no history of lead exposure generally have concentrations in liver tissue of <2 ppm in wet weight and more frequently <1 ppm [
The hepatosomatic index (HSI) was 1.57% ± 0.11%, (se) which is lower than one reported by Ross [
We found that only one individual contained lead pellets in the gizzard representing an incidence of 5.5%, and we did not observe any proventricle or gizzard lesions related to shooting. It was possible that pellets were ingested just before the time of collection, maybe 2 or 3 days earlier. This assumption is based on the fact that geese were collected during the first visit by hunters and based on the state of little dissolution of lead particles found and we confirmed it whit relevant results from histopathological analysis or hepatosomatic index.
Acid conditions (pH 2.5) in geese stomachs may facilitate lead dissolution, which produces toxic lead salts that are absorbed into the bloodstream. Lead traces can remain in the gizzard for approximately 6 weeks after ingestion, with an average retention of 18 to 21 days. When lead particles are discarded immediately after intake, only a small amount of lead is absorbed [
It is important to remark that the presence of shotgun pellets in geese gizzards does not necessarily indicate lead poisoning. The absorption and tolerance to lead depends primarily on two factors, namely concentration and exposure time. These factors are determined by the size and number of pellets ingested, age and sex of the bird, as well as composition and volume of food ingested [
Histological lesions in liver tissue when lead poisoning has occurred consist of blood cells infiltrated in the parenchyma, generalized hemosiderosis and acidophilic bodies at cytoplasmic level [
Results obtained in this study did not showed evidence of lethal or sublethal effects caused by lead poisoning. However, the possibility of this risk due to the presence of lead shots in the digestive tract of some birds can not ruled out.
We thank Dr. J. Herrera Corral for his support in lead contents analysis, and we also thank MVZ J. Breton for his help and support in providing the geese. This manuscript has benefited by comments from Dr. H. Weir.