Sublethal Concentrations Of Zinc Research Articles

HISTOPATHOLOGICAL CHANGES ON ETROPLUS MACULATUS (BLOCH, 1795) DUE TO ZINC EXPOSURE

The contamination of the aquatic systems with heavy metals from natural and anthropogenic sources has become a global problem which poses serious threats to ecosystems and natural communities. Heavy metals get bio concentrated in organisms that may cause health problems in humans via the food chain. The heavy metal zinc causes most serious environmental contaminations and effects due to its rampant use. In this study sublethal effects of the heavy metal, zinc on the histopathological parameters in fresh water fish, Etroplus maculatus was investigated. The 96 hour LC50 value of zinc was determined by Probit analysis, that was found to be 12.4 mg/L. The liver and kidney samples were collected from fish was exposed to sublethal concentrations of zinc on 14th and 28thdays.The structural deformities observed in the liver tissue showed swelling of hepatocytes, vacuolar degeneration, necrosis, nuclear hypertrophy and cirrhosis with acute haemorrhage where as, kidney showed degenerated renal capsule and renal tubule, edema, necrosis and haemorrhage in the interstetium. The histpathological changes become prominent as the days and concentration of exposure increases. The study thus establishes that zinc is harmful to Etroplus maculatus even in sublethal concentrations and effective management strategies are to be evolved and implemented to protect our water bodies and the organisms from problems of heavy metal pollution.

RECORDED CHANGES IN SOME BIOCHEMICAL INDICATORS OF GRASSCARP CTENOPHARYNGODON IDELLA EXPOSED TO MERCURY AND ZINC

^J.rass carp Ctenopharyngodon idella, fingerlings were exposed to lethal and sublethal concentrations of mercury and zinc. The changes in haemoglobin (Hb) haematocrit (Ht), osmolality, branchial Na+-K+-ATPase5 acetylcholinesterase (AchE), sodium (Na*); potassium (K*) and water content were recorded. Blood Hb and Ht showed a general trend of significant decrease in exposed to lethal and sublethal concentrations of mercury and zinc. The serum osmolality showed a significant increase on exposure offish to lethal and sublethal concentrations of mercury and zinc. In fishes exposed to lethal concentration of mercury and sublethal concentration of mercury and zinc, the activity of branchial Na+-K+-ATPase was increased, while in case of lethal exposure to zinc, the enzyme activity was reduced. Serum AchE activity decreased in exposed to lethal concentration of mercury and sublethal concentration of zinc. On the other hand, the enzymatic activity was increased in fishes exposed to lethal concentration of zinc and sublethal concentration of mercuiy. In case of brain, the AchE activity increased in fishes exposed to lethal concentration of mercury and zinc and decreased in fishes exposed to sublethal concentration of mercuiy and zinc. The concentrations of (Na+, K4) in serum, liver and muscle were significantly increased when fish were exposed to either lethal or subletlial treatments. The water content of liver

Effect of zinc on maturation and breeding potential of Cyprinus carpio and Cirrhina mrigala

Effects of safe and sublethal concentrations of zinc were observed on ovarian maturation and breeding potential of carps. Exposure of Cyprinus carpio to 56 and 100 μg/L and Cirrhina mrigala to 560 and 1000 μg/L of zinc for 60 days during each of the preparatory and prespawning phases of reproduction revealed concentration dependent decline in gonado‐somatic index, ova diameter and absolute fecundity complemented with decline in total proteins and total lipids in the ovaries. Exposed fishes were also induced to breed except C. carpio exposed to sublethal concentration.

Survival time modeling of exposure of juvenile atlantic salmon ( Salmo salar) to mixtures of aluminum and zinc in soft water at low pH

The toxicity of mixtures of aluminum and zinc to juvenile Atlantic salmon ( Salmo salar) was studied in low ionic strength waters similar to those encountered during spring snowmelt in salmon rivers on the Canadian Precambrian Shield. Fish were exposed to environmentally realistic concentrations of inorganic monomeric Al singly (≤ 15 μM), and to mixtures of Al and a sublethal concentration of zinc (1.7 to 0.8 μM), at three acidic pH levels (pH 4.5, pH 4.8 and pH 5.2). For Al-only and Zn-only exposures, the LC-50(M) values exhibited a marked pH dependence (higher values at low pH); even when expressed in terms of the free-metal ions (Al 3+ or Zn 2+), to take into account the influence of pH changes on metal speciation, the LC-50(M z+) values were still different at each pH. Modification of the free-ion activity model, to include competition between the proton and the free-metal ions at the gill surface, can explain part of this pH dependence, but there remains some residual dependence on the H +-concentration. as yet unexplained. Fish mortality data at each pH exposure were also modeled with a Cox proportional hazards model. In all cases, the presence of Zn reduced survival times in the Al + Zn mixtures, despite the use of sub-lethal Zn concentrations (only 0.1–0.2 toxic units). Survival time modeling indicated a simple additive mode for the toxicity of the Al + Zn mixture; models with the best fit included a covariate term for Al (either as Al 3+ or as inorganic monomeric Al) and a classification code variable for Zn.

Toxicity in Tilapia zilli and Clarias lazera (Pisces) induced by zinc, seasonally

1. 1. Subadult teleosts, Tilapia zilli and Clarias lazera, were exposed in laboratory bioassays to lethal and sublethal concentrations of zinc, seasonally (at range of temperature between 9.3 ± 1.5 and 25 ± 1°C). 2. 2. It appears that Tilapia is more susceptible to Zn than Clarias and both species are more resistant to Zn toxicity at lower temperature (during winter). 3. 3. To determine the uptake and tissue distribution of Zn in the two species, gill, liver and muscles were analysed at moderate temperature (during spring). After a 96 hr exposure period, Zn was decreased in the following order: gill ⪢ liver ⪢ muscle.

Uptake and excretion of zinc by several tissues of the lobster (Homarus Americanus)

Lobsters, Homarus americanus, were exposed in a flow-through system to a sublethal concentration of zinc (Zn++) for 4 d and then transferred to flowing unspiked sea water for 7 d. The concentrations (μg/g dry weight) of Zn++ after the four days of exposure were in the order gill > green gland > haemolymph > hepatopancreas > crusher tissue > crusher muscle > pincer tissue > shell > testes > heart > pincer muscle > abdominal (tail) muscle. After 7 d in unspiked water the concentration of Zn++ in each of the tissues decreased, but did not return to pre-exposure levels. In terms of the total tissue burden the level of Zn++ in only the hepatopancreas continued to increase during the depuration phase. The data were analysed using a four-compartment model with haemolymph as the “central” compartment. The exchange of Zn++ between gills and water was rapid, between gills and haemolymph was somewhat slower, and between haemolymph and tail muscle was extremely slow.

Detoxication of zinc and cadmium by the freshwater protozoan Tetrahymena pyriformis: II. Growth experiments and ultrastructural studies on sequestration of heavy metals

Sublethal concentrations of zinc and cadmium limited the growth of batch cultures of the ciliate Tetrahymena pyriformis. Electron microscopy of cultured populations revealed many electron-dense cytoplasmic granules in cells exposed to zinc (60 ppm), but fewer in cells grown with less zinc (6 ppm) or cadmium (2 ppm). Ultrastructural abnormalities were observed only in cells grown with cadmium. These contained autophagic vacuoles and had damaged nuclei. Zinc was shown to exert a protective effect against cadmium toxicity both in terms of growth and ultrastructural appearance. Electron probe X-ray microanalysis revealed both zinc and cadmium within the cytoplasmic granules of cells exposed to these metals. Since the granules are normally composed predominantly of calcium and magnesium, these ions are implicated in the intracellular detoxication of zinc and cadmium. Zinc was detected only in the granules, while cadmium was also found in autophagic vacuoles and damaged nuclei.

The activity of delta 5-3 beta hydroxysteroid dehydrogenase enzyme in the interrenal tissue of rainbow trout (Salmo gairdneri Richardson) exposed to sublethal concentrations of zinc.

The effects of exposure of rainbow trout (Salmo gairdneri Richardson) to three sublethal concentrations of zinc (0.248, 0.528 and 1.14 ppm) on delta 5-3 beta-hydroxysteroid dehydrogenase (delta 5-3 beta HSDH) enzyme activity in the head kidney tissue was investigated. The activity of this enzyme was localized by the reduction of a tetrazolium salt to formazan at the site of activity. Using subjective methods to indicate the degree of activity and indirectly assess the degree of corticosteroid production, the zinc-exposed rainbow trout showed a greater degree of delta 5-3 beta HSDH activity compared to the control fish. This increase in enzyme activity has been associated with the stimulation of the pituitary-interrenal axis by the noxious stress of zinc.

The effect of sublethal concentrations of zinc on growth and plasma glucose levels in rainbow trout, Salmo gairdneri (Richardson).

The long term effects of three sublethal concentrations of zinc (0.214, 0.52 and 1.12 ppm) on growth and plasma glucose concentration in yearling rainbow trout Salmo gairdneri (Richardson) were investigated. Analysis of covariance of percent weight increase revealed that a significant inhibition of growth (P less than 0.05) in the 1.12 ppm zinc-exposed fish had occurred. Plasma glucose showed a significant hyperglycemia (P less than 0.05) in all three zinc-exposed groups of fish after 7 days exposure and in the 1.12 ppm zinc-exposed group after 63 days. The hyperglycemia observed has been explained as possibly resulting from activation of the pituitary-interrenal axis by the stress of zinc causing mobilization of tissue glycogen.

Mortality Curves of Bluegills (Lepomis macrochirus Rafinesque) Simultaneously Exposed to Temperature and Zinc Stress

Bluegills were exposed to a temperature-zinc interaction consisting of five temperature regimes and four concentrations of zinc which were 1.0, 5.6, 10.0 and 32.0 mg Zn++/1. All of the above concentrations of zinc and a control were tested on five groups of fish which had been acclimated to (1) 20 ± 1 C, (2) 30 ± 1 C and fish which had been acclimated to 20 ± 1 C and were exposed to temperature increases at the following rates: (3) 1 C/24 hours, (4) 1 C/1 hour and (5) 1.5 C/10 minutes until a maximum of 30 C was reached. This study showed that a rise in temperature could reduce the survival time of bluegills exposed to lethal and sublethal concentrations of zinc. Reductions in survival time were a function of the rates at which the temperature was increased. For example, bluegills acclimated to 20 and 30 and then exposed to a lethal concentration of zinc (32 mg Zn++/1) at each temperature died 2.6 times faster at 30 C than at 20 C. Fish acclimated to 20 C and exposed to a temperature increase of 1.5 C/10 minutes died 4.8 times faster than fish maintained at 20 C. A sublethal zinc concentration (5.6 mg Zn++/1) produced no mortalities in 20 C acclimated bluegills in 96 hours but was toxic to fish when the temperature was increased from 20 to 30 C at a rate of 1.5 C/10 minutes.

Hybridization Studies on a Zinc-Induced Variant of Hypomyces Ipomoeae

SUMMARYA striking variant has been produced by cultivation of monoploid hyphae of Hypomyces Ipomoeae on medium containing a sub-lethal concentration of zinc nitrate.Analyses of 5 consecutive single-conidium culture-series, consisting of 25 cultures each, have proved the mutant strain, aborta, to be homocaryotic. Single-conidium and mass-transfer cultures of the aborta strain have shown a high degree of uniformity.The most striking feature associated with the variant was that four, rather than eight, spores were formed in aborta × normal asci, due apparently to inability of nuclei carrying the aborta factors to delimit spores.Evidence strongly indicated that in rare instances ascospores in aborta × normal asci may include more than one of the eight nuclei resulting from maturation of the zygote nucleus. Thus, in two instances, single ascospores isolated from hybrid perithecia yielded mixed cultures containing both normal and aborta hyphae. The two fx aborta strains thus obtained bore opposite sexual-reaction factors. In two other instances, single ascospores from hybrid perithecia yielded cultures containing normal hyphae of both sexual reactions, as was evidenced by the appearance of fertile perithecia in both cultures.The inability of aborta nuclei to delimit ascospores may be attributed to the inactivation or to the deletion of one or more genes determining ascospore delimitation. The ascospore-delimitation factors and the sexual-reaction factors are in different linkage groups.The genie alteration or mutation, although having occurred on medium containing a sub-lethal concentration of zinc, cannot be considered a specific effect of zinc ion without further evidence.