Consequences of trace metal cocktail exposure in zebra finch (Taeniopygia guttata) and effect of calcium supplementation
Trace metal elements are significant stressors in urban areas. Their harmful effects on physiological parameters are demonstrated, but current laboratory studies are not representative of wild chronic exposure to a trace metal cocktail. Calcium can reduce the accumulation and toxicity of several metals, but soil acidification in cities leads to a decrease in bioavailability of this element. The objective of this study was to investigate the accumulation and toxicity of a trace metal cocktail representative of urban exposure on passerine birds, and test the importance of calcium availability on these toxic effects. We exposed zebra finches (Taeniopygia guttata) to a cocktail of metals and metalloids in drinking water, with or without calcium supplementation. We monitored the concentration of metals in the blood and feathers, and their effects on oxidative status, and telomere length. The metal cocktail led to higher concentration of all elements in the feathers, and of arsenic and lead in the blood. Birds with a higher concentration of cadmium, arsenic and lead in the feathers had shorter telomeres, but no impact of the cocktail was detected on the oxidative status. Birds of the ‘calcium’ group and the ‘calcium and metal’ group accumulated higher concentrations of zinc, chromium and nickel in feathers. The ‘calcium and metal’ group also accumulated lower concentrations of arsenic and lead in feathers compared to the ‘metal’ group. Our results suggests that chronic exposure to a cocktail of metals at low concentrations has deleterious effects on birds, which can be limited through calcium intake. Methods 4 groups of 10 birds were exposed to 4 treatments: 'Ctrl’= control group with low-Ca diet and no trace metal element (TME), ‘TME’= birds with low–Ca diet exposed to a TME cocktail, ‘Ca’= rich-Ca diet and no TME and ‘TME+Ca’= rich-Ca diet and TME cocktail. The TME cocktail contained both essential TME (i.e, necessary for biological process) and non-essential metals and metalloid: 10 ppm of Pb , 0.7 ppm of Cr, 1 ppm of As, 100 ppm of Zn, 24 ppm of Cu, 0.5 ppm of Ni, 0.2 ppm of Co, and 0.1 ppm of Cd. At day 0, tarsus length was measured with a calliper (±0.1 mm). Every two weeks we measured body mass (±0.1 g) with a precision scale and collected 100 µL of blood from brachial vein (in 2 tubes of 50 µL) with heparinized capillary to measure physiological parameters (free, oxidised and total glutathione, glutahione peroxidase activity, dosage of reactive oxygen metabolites, and relative telomere length) and concentrations of metals (ICP-MS analyses). At day 0 and 29 we also collected the right fourth primary feather for metal analyses (ICP-MS analyses). For blood, several samples had metal concentrations under the limit of detection. To take these data into account, we used a statistical method for left censored data with a specific package : NADA package which requires pre-processing of data. It corresponds to the last 16 columns of this file.