Use of Metal-Rich Slag as a Source of Grit and Its Effects on Pigeon Health and Fitness

Abstract

Uptake, utilization and physiological effects of slag as a source of grit were studied in laboratory pigeons provided with an ad libitum supply of a) industrial metal-rich slag b) pristine gravel or c) a combination of the above, over a one-year period. Although retention times undoubtedly differed, both grit types appeared to remain within the gizzard until near-completely abraded, thus resulting in near-maximal exposure of the bird to intrinsic metal loads present. Mortalities were confined to the slag-treated group (62%) and birds given choice (11%) with no deaths among gravel-treated controls. Surviving slagtreated birds indicated marked weight increases in both liver (2-fold) and kidney (~ 46%) whereas body fat scores and breast muscle mass were substantially reduced. Slag ingestion likewise affected marked hypertrophy of the parathyroid glands. Tissue metal assays indicated a striking accumulation of Fe (7-8 fold) in liver, and to a lesser extent in bone (3.2-fold) and kidney (1.5-fold) of slag-treated birds. Histologically, hepatocytes and invading clusters of macrophages appeared stuffed with numerous pigmented cytoplasmic granules-histochemically identified as predominantly stored Fe. These findings point to the development of an acute toxic Fe storage condition, not unlike avian hemosiderosis (iron storage disease), as the prime cause of morbidity and eventually death of these slag-treated birds. Long bones of slag-treated birds were substantially more pliable, of reduced strength, and characterized by significantly reduced Ca levels compared to control birds. Histological examination of keel and tibiotarsal bones revealed moderate to severe mineral resorption, with thinning of cortical layers in lamellar bone and reduced cross-strut formation in cancellous bone. Evidence of active woven bone formation at these foci was likewise confirmed, thus corroborating the marked hypertrophy of parathyroids and implied changes in parathyroid function. Given free choice, birds were basically nonselective, rather than exclusive, in their uptake of gravel versus slag. Given that slag was not avoided, and in light of its profound adverse physiological effects, concern for the ecological implications of the vast quantities of exposed slag within our environment and its potential health risks to wild bird populations is warranted.

Mechanical, Chemical, Structural, and Radiological Changes in Pigeon Bone, Associated with The Dietary Intake of Nickel Recovery Slag

“…1.9785 ± 0.1948 (n = 9) 1.7698 ± 0.2223 (n = 9) 0.0251 BMD (g/cm 2 ) 0.152 ± 0.005 (n = 6) 0.143 ± 0.005 (n = 6) 0.0089 Ca (ppm) 82621.8 ± 11046.7 (n = 9) 70912.8 ± 11952.7 (n = 9) 0.0272 Fe (ppm) 80.87 ± 37.41 (n = 9) 242.76 ± 190.35 (n = 9) 0.0127 BS (N) 451.57 ± 133.78 (n = 7) 328.50 ± 139.62 (n = 8) 0.0500 YM (MPa) 3483.6 ± 1853.7 (n = 7) 2835.9 ± 879.6 (n = 8) 0.0662 changes may also be indicative of cortical discontinuities, foci of woven bone formation, and/or spicules of fibroplasia, consistent with previously reported histological findings [1]. Brissot et al described generally similar changes in bony structures in humans subjected to iron overload conditions [25].…”

“…Most birds -and granivorous species in particular -depend on a continuous uptake of pebble-sized grit to assist in the grinding functions of the gizzard, and are known to routinely obtain such pebbles from available sources within their home range environment. In this work, we extend previous work and analyze the effects of slag ingestion through diet, on seven different quantitative, and two qualitative parameters of the tibio-tarsal bones in pigeons (Columbia Livia Domestica) [1]. The specimens were divided into a control group (n = 9), which were provided a (normal) grit source of pristine limestone, and an experimental group (n = 9) fed slag-based grit, both for a period of 1 year.…”

“…The specimens were sacrificed and frozen after one year of controlled feeding. Selection, feeding, and husbandry of the specimens have been previously described [1]. Tibio-tarsal bones were excised from the frozen birds.…”

“…Slag tailings containing high concentrations of base metals from over 130 years of continuous nickel smelting operations in the Sudbury, Ontario basin in Canada, have become ubiquitous. Among its engineering uses are road construction, laying of railway beds, bridge building, construction of retaining buttresses, break walls, causeways, and dikes, surface stabilization of inclines and ravines, production of cement and concrete aggregates, and occasional use as a base substrate for parking lots and airport runways [1,2]. This material rich in heavy metalsparticularly iron -upon ingestion has the potential to effect physical, radiological, chemical, mechanical, and structural changes in bony structures of biological systems.…”

“…This material rich in heavy metalsparticularly iron -upon ingestion has the potential to effect physical, radiological, chemical, mechanical, and structural changes in bony structures of biological systems. Micro chemical analysis has revealed that Sudbury basin nickel recovery slag contains approximately 34.7 ± 0.6% Fe by weight [1]. Most birds -and granivorous species in particular -depend on a continuous uptake of pebble-sized grit to assist in the grinding functions of the gizzard, and are known to routinely obtain such pebbles from available sources within their home range environment.…”