Effect Of Zinc Contamination Research Articles

Effects of zinc contamination on a natural nematode community in outdoor soil mesocosms.

The effect of zinc on the indigenous nematode fauna of a sandy soil was determined in an experimentally contaminated outdoor field plot. The aims of the study were to describe and quantify the changes in density of separate nematode taxa and total nematodes, and the changes in the number of taxa, species diversity, community maturation, and species composition in response to zinc exposure with time, and to compare the observed responses with benchmark concentrations for soil as derived from the species sensitivity distribution (SSD) for zinc toxicity. Speciation of zinc in pore water was considered and CaCl2-exchangeable zinc concentrations were used as a measure of the bioavailable zinc fraction. After contamination, a reduction of total zinc and an increase of labile sorbed zinc over time occurred, concurrent with various changes in soil and biological characteristics. Data analyses on the nematode species revealed different sensitivity levels for several population and community endpoints to zinc exposure. Based on no observed effect concentration (NOEC) values, the most sensitive community-level response was obtained with principal response curve (PRC) analysis, which incorporates all density data in a single analysis. The PRC-based community NOECs were 56, 100, and 100 mg total Zn/kg dry soil after 3, 10, and 22 months of exposure, respectively. Based on 0.01 M CaCl2-exchangeable zinc, the community response appeared to increase, as NOECs were 4.9, 4.4, and 0.67 mg exchangeable Zn/kg dry weight. Total density was least sensitive, followed by diversity of taxa and the Shannon-Wiener index. NOECs for separate species covered a broad range from sensitive to tolerant species. This range of sensitivities was similar to the one found for other species groups tested in the field plot soil. A comparison was made between benchmark concentrations HC5 and HC50 derived from the general SSD of soil organisms for zinc and the nematode response data. These comparisons roughly confirm the predictions of the SSD model, that is, the community NOEC is in agreement with the benchmark that should protect the soil ecosystem's integrity, and large adverse effects were found at the benchmark derived for setting remediation urgency.

The effect of zinc contamination from electricity pylons. Genetic constraints on selection for zinc tolerance

Zinc tolerance, based on root growth in zinc-containing solutions, was examined in samples of 30 Agrostis capillaris L. individuals collected from populations beneath five electricity pylons in North Wales. The populations were found to vary in zinc tolerance. Three of them contained individuals whose tolerance ranged from low to high, one population consisted of individuals with low to moderate tolerance, whilst the fifth population (ZK-180) contained no tolerant individuals. Differences in zinc tolerance were also found between seedlings raised from five seed populations collected from plants growing in the uncontaminated pasture areas adjacent to four of those pylons, and one further pylon in the same area. The population adjacent to pylon ZK-180 consistently showed little sign of tolerant individuals. Samples of seeds collected from the populations in the uncontaminated areas surrounding each pylon, and likely to have been the origin of the pylon populations were grown at a concentration of 15 μg Zn cm−3, and root lengths of 105 randomly chosen seedlings from each were measured. The means and variance of tolerances of four of the five did not differ, but all were significantly higher than that adjacent to pylon ZK-180. Two cycles of selection and breeding for increased zinc tolerance were carried out using seed samples collected from four of the five populations of adults collected beneath pylons examined previously, and including population ZK-180. Marked increases in tolerance were effected in three of the four populations; no corresponding increase in tolerance was achieved for population ZK-180. It is concluded from these findings that the lack of zinc tolerance beneath pylon ZK-180 is due to the absence of appropriate variation in zinc tolerance within that population, and in potential colonizing material adjacent to it, a situation which contrasts with that for the other three pylons.

The effect of zinc contamination from electricity pylons. Contrasting patterns of evolution in five grass species

SUMMARYSamples of 8–35 individuals of Agrostis capillaris, A. stolonifera, Anthoxanthum odoratum, Deschampsia cespitosa and Festuca ovina were collected from zinc‐contaminated soils beneath electricity pylons erected in North Wales and Lancashire between 1956 and 1970. Their zinc tolerance was assessed, as was that of two individuals of the same species collected from adjacent uncontaminated soils. Five soil samples from beneath each pylon were collected for evaluating total and extractable soil zinc, soil pH, and soil organic matter.Some degree of zinc tolerance was detected in all five species, suggesting that evolution of tolerance has taken place relatively rapidly, particularly in A. capillaris, D. cespitosa, and Anthoxanthum odoratum. However, tolerant individuals of all species were not found beneath all pylons even when the species was present in the surrounding vegetation. This confirms and extends to other species previous findings in A. capillaris, that the gene or genes necessary for the evolution of tolerance are not universally present within species.

The effects of zinc contamination from electricity pylons – evolution in a replicated situation

summaryMost electricity pylons are zinc coated. It might be possible for this to cause zinc contamination of soil beneath the pylons sufficient to impose selective forces by which zinc‐tolerant populations would develop in a replicated manner. An investigation of Agrostis capilluris L. populations sampled under a series of pylons in North Wales shows that: Zinc concentrations are considerably greater in soils beneath pylons, particularly adjacent to pylon legs. Soils sampled under different pylons had mean zinc concentrations varying from 1250 ± 200 to 6500 ± 4000 μg−1 as total, and from 570 + 188 to 3000 ± 2000 μg g−1 as acetic acid extractable. In control soils, comparable values were from 170 ± 35 to 320 ± 90 μg g−1 total zinc, and 70±10 to 140 ± 30 μg g−1 acetic acid‐extraetable zinc. Zinc toxieity is found in such soils causing significant reduction in plant dry weight and tiller production of normal material of A. capillaris. The pattern of root growth response to increasing zinc concentration in solution culture of samples of adult plants collected from beneath pylons differed significantly. Some individuals had zinc tolerance equivalent to that of zinc mine plants; others had low but measurable tolerance; others differed little from plants from uncontaminated control sites. These results clearly show that evolution of zinc tolerance has occurred rapidly, since the pylons sampled were all less than 30 years old, but the outcome is different under different pylons, almost certainly because of differing genetic constitutions of different founding populations.