Egrets as Monitors of Trace-Metal Contamination in Wetlands of Pakistan

Abstract

Environments in Pakistan are subject to increasing pollution, but previous studies were very scanty. During 1999 and 2000, we assessed trace element contamination at three wetlands, Karachi Harbour (with presumed industrial-urban pollution), Taunsa Barrage (agricultural pollution), and Haleji Lake (relatively unpolluted), using as indicators the eggs and the feathers of colonial waterbirds, particularly Little Egrets, their prey, and the sediments collected within their foraging areas. The concentrations of As, Cd, Cr, Pb, Hg, Mn, Se, and Zn were generally within the normal background level, and mostly below the threshold that may affect bird survival or reproduction. However, somewhat high concentrations were found in fish from Karachi, for Pb that was at levels that may harm fish reproduction, and for Hg that was at limit concentration for human consumption. Alarming concentrations were found for Cr and Se in sediments from Karachi, that were above the critical levels for contaminated soil, and Se in eggs, that may affect egret reproduction. The differences among the three wetlands were less marked than hypothesized. The egret species within the same area differed in the concentration of certain elements in their eggs, possibly because females may have foraged in different habitats before breeding, whereas no interspecies difference was found in chick feathers, presumably because their food had been collected in similar habitats around the colony. High bioaccumulation from sediments to organic samples occurred for Hg, while Cd, Se, and Zn exhibited low accumulation; for all these elements, feathers of predatory birds such as the egrets are the best indicators of environmental contamination. On the other hand, As and Cr did not bioaccumulate, and the sediments, or the organisms low in the food chain, like fish or crustaceans, are better indicators of their presence in the environment than predatory birds.

Estimation of heavy metal residues from the feathers of Falconidae, Accipitridae, and Strigidae in Punjab, Pakistan

“…Conversely, Malik and Zeb (2009) reported greater accumulation of Cd, Zn, and Pb and lower levels of Ni and Cu in the feather samples of Cattle Egrets from Chenab and Ravi rivers (central Punjab) and Lake Rawal, Islamabad (northern Punjab) as compared to the results of the current study. Similarly, the levels of As in the current study were much higher than those estimated by Boncompagni et al (2003) from Karachi and southern Punjab. The trophic level of egrets is, however, different from that of raptors and perhaps this comparison is not very suitable but still it provides some information regarding the greater levels of metals.…”

“…This indicates that for the last 10 years the levels of these metals have increased considerably in the environment, especially in this part of the country. Estimates of Cd concentrations in feathers of Little Egrets and Cattle Egrets by Boncompagni et al (2003) from Lake Haleiji (0.09 µg/g), Karachi (0.10 µg/g), and Taunsa Barrage (0.06 µg/g) were lower than the levels of metals obtained in the current study for southern (1.83 µg/g), central (3.35 µg/g), and northern (1.14 µg/g) areas, indicating a greater load of heavy metal pollution in recent times. Conversely, Malik and Zeb (2009) reported greater accumulation of Cd, Zn, and Pb and lower levels of Ni and Cu in the feather samples of Cattle Egrets from Chenab and Ravi rivers (central Punjab) and Lake Rawal, Islamabad (northern Punjab) as compared to the results of the current study.…”

Elemental composition in feathers of a migratory passerine for differentiation of sex, age, and molting areas

“…The elemental profile of a feather may reveal information on the geographic origin of a bird provided that there are elemental differences between molting areas. Factors such as age, sex, species, metabolism and molting locations were demonstrated to influence the trace element composition in feathers (Bortolotti and Barlow 1988;Bortolotti et al 1990;Boncompagni et al 2003;Szép et al 2003;Donovan et al 2006). The stable isotope composition mainly differs on continental or regional habitat scale (Hobson 2005).…”

Assessment of Trace-Metal Concentrations in Western Reef Heron (Egretta gularis) and Siberian Gull (Larus heuglini) From Southern Iran

“…These species can provide interesting data to monitor the quality of the environment (Kim and Koo 2008). Many studies have recommended herons and egrets as bioindicators for heavy metals in aquatic systems and local pollution around breeding sites (Kim and Koo 2007;Boncompagni et al 2003). Because herons and gulls are at the top of their trophic level and can yield information over a large area around each sampling site, they provide information not only on bioavailability of contaminants but also on how, where, and when they are transferred within the food web (Battaglia et al 2005).…”