Abstract

China’s burgeoning population and rapidly growing economy have produced an environment with potential to adversely affect health and welfare of humans and indigenous wildlife. The rise of industrialization, use of coal as a prime energy source, mining, smelting, sewage irrigation, and municipal sludge applications to soil are major contributors of pollutants.² Two species of bamboo (Chimnobambusa sp. and Pleiobastus sp.) collected in the Wolong National Nature Reserve in Sichuan Province and shipped (with giant pandas) to the National Zoological Park (NZP) in Washington, DC had a black surface residue. Concerns that this residue might be harmful led to analyses (using the Association of Official Agricultural Chemist procedures) for cadmium (Cd), mercury (Hg), and lead (Pb). For comparison, four species of bamboo (yellow groove [Phyllostachys aureosulcata], bissetii [Phyllostachys bissetii], black [Phyllostachys nigra], and arrow [Pseudosasa japonica]), growing at the NZP, were cut about 50 cm above ground level (to minimize soil contamination) and analyzed for the same elements. Representative plants (at least three of each species) were separated into species composites of leaves, stems, and culms (only leaves and culms for arrow), and these plant parts were analyzed separately. Maximum tolerable mineral levels (MTLs) for animals, as defined by the National Research Council (NRC),³ vary with chemical form and solubility, animal species, composition of diet and water, and indices of toxicity. MTLs in dietary dry matter (DM) for chronic exposure range from 1 to 10 ppm for Cd, 1 to 2 ppm for Hg, and 0.5 to 45 ppm for Pb. Concentrations of Cd in DM of Chimnobambusa leaves, stems, and culms were 0.45, 0.40, and 0.25 ppm, respectively—higher than levels in all tissues of any other bamboo species except for Pleiobastus culms, which contained 0.27 ppm. Concentrations of Hg were higher in Chimnobambusa leaves (0.05 ppm) than in leaves of other species (0.03–0.04 ppm) but were <0.025 ppm in stems and culms of all species tested. Concentrations of Cd and Hg in all bamboo tissues were below their respective MTLs.

Concentrations of Pb in DM of leaves, stems, and culms of Chimnobambusa were 17,500, 6,630, and 2,950 ppm, respectively, and in Pleiobastus leaves, stems, and culms, 3,880, 5,060, and 439 ppm, respectively. Such high levels should be of concern if fed to giant pandas in China, but Pb concentrations in bamboo from NZP grounds also were higher than the NRC MTLs, ranging from 363–1,610 ppm in leaves, 132–574 ppm in stems, and 33–337 ppm in culms. The highest values were found in leaves of arrow and bissetii bamboo growing 6–23 m from a commissary and maintenance area with high vehicular traffic and where painting, welding, fueling, and vehicle repair take place. To minimize dietary exposure of NZP pandas to heavy metals, bamboo for feeding is harvested largely from agricultural areas relatively remote from heavily traveled roadways. No reports of lead toxicosis in giant pandas have been found. However, ponies consuming grass hay grown in northern Idaho near a silver mine and a lead/zinc smelter, and contaminated with Pb and Cd (423 and 10.8 ppm as fed, respectively), exhibited declines in hematocrit, some Howell-Jolly bodies and nucleated erythrocytes in peripheral blood, weakness, and slight incoordination. These signs progressed to difficulty in prehension and swallowing and impaired muscle control of the lips and anal sphincter. Ultimately, periodic fine muscular tremors, severe incoordination, and esophageal paralysis were seen.¹ These and additional toxicity signs, such as cardiovascular pathology, nephrotoxicity, altered immune function, decreased reproductive efficiency, and impaired bone growth and remodeling have been attributed to excess Pb exposure in other species.³

Neurologically, lead blocks voltage-regulated calcium channels, thus inhibiting the influx of calcium that promotes release of neurotransmitters.³ It also competes with calcium for binding sites on receptor proteins that have secondary messenger functions, such as calmodulin and protein kinase C. Lead also competes with iron for ferritin-binding sites. A number of toxic mechanisms have been proposed, but lead’s ability to mimic the action of calcium has stimulated use of higher dietary calcium levels to decrease intestinal absorption of lead and to modulate its toxicity. Potentially important interactions of magnesium, zinc, selenium, vitamin E, vitamin C, and vitamin D with Pb absorption or metabolism have been reported.³

Acknowledgments

The authors wish to thank Lisa Stevens, B.S., Curator of Primates and Pandas at the National Zoological Park, Washington, DC for her assistance in obtaining the bamboo samples from China, and the volunteers from Friends of the National Zoo who helped with the extensive processing of samples in the laboratory.

Literature Cited

1.  Burrows, G.E., and R.E. Borchard. 1982. Experimental lead toxicosis in ponies: comparison of the effects of smelter-effluent contaminated hay and lead acetate. Am. J. Vet. Res. 43:2129–2133.

2.  Han, F.X., A. Banin, Y. Su, D.L. Monts, M.J. Plodinec, W.L. Kingery, and G.E. Tripplet. 2002. Industrial age anthropogenic inputs of heavy metals into the pedosphere. Naturwissenschaften. 89:497–504.

3.  National Research Council. 2005. Mineral Tolerance of Animals, 2nd revised edition. National Academies Press, Washington, DC.