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Determination of toxicity to an invertebrate population.

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Introduction

Determination of Toxicity to an Invertebrate Population Aim The aim of this experiment is to observe how increasing concentrations of copper (II) sulphate pentahydrate solution affect the mortality of Daphnia (freshwater zooplankton). Introduction Toxicity is deemed to mean 'the inherent poisonous potency of a substance' (lecture notes). Freshwater pollutants are extremely diverse and are described by Jeffries and Mills (1990, p135) as "anything in the wrong place, in damaging quantities". Toxic pollutants cover a wide range of substances, substances that have no normal place in natural systems and many of which are man made (Jeffries & Mills, 1990). These pollutants include metals, organic compounds, gases, anions, radioactive material and acids and alkalis and can enter freshwater systems by means of domestic, industrial or agricultural effluents. Metals are often leached from mineworkings (Mason, 1991). Toxicity has been described to have two main effects on living organisms, acute toxicity, which has been defined as a dose of poison administered in a short period of time, being generally lethal and chronic toxicity, which refers to a relatively low dose being administered over a prolonged period, being lethal or sub-lethal (Gilbertson, Kent and Pyatt, 1989). The toxicity of most poisons can be affected by the environment with factors involved being, temperature, oxygen content, pH and dissolved salts (Haynes, 1971). Results of toxicology studies on organisms can be expresses as lethal dose (LD) or lethal concentration (LC), where death is the criterion of toxicity. ...read more.

Middle

It has been shown that many poisons have been known to increase each other's toxicity, so the LC50 of copper (II) sulphate in the laboratory may not be correct for freshwater purposes (Haynes, 1971). Another difficulty is the interpretation of results. It is relatively simple to find out how many Daphnia die in different concentrations of copper (II) sulphate when testing in the laboratory, but when in 'real-life' conditions, it is possible that the Daphnia would survive longer than 30 minutes with the dilution occurring in the water in their natural environment. There are many other factors that have an effect on freshwater organisms that are difficult to replicate in a laboratory. The toxicity of most poisons is largely affected by environmental factors. Temperature has a great effect on toxicity as, in general, "at a given concentration of poison, a rise of 10oC halves the survival time" (Haynes, 1971, p75). The increase in temperature can affect the metabolic activity and behaviour of an organism and it can also alter the physical and chemical state of the pollutant (Mason, 1991). It can, therefore, be suggested that many poisons may become more poisonous during summer. This would be very difficult to replicate in a laboratory. The decrease in the content of oxygen in the water can have an effect on the toxicity of substances. It is understood that several poisons become more toxic at low oxygen concentrations. ...read more.

Conclusion

I would not say that this experiment was very successful, although it does indicate why experiments like this are so difficult to replicate in a laboratory. Conclusion In conclusion, it is possible to see from the results and from general written text that the higher the concentration of toxin, the greater effect is has on the mortality of, in this case, Daphnia. Pollution is a general concern in the threat to wildlife, humans and the planet. Man's resources are being damaged by pollutants. Careful observation and preventative measures need to be undertaken to prevent further damage. Pollutants being released from petrol stations, oil refineries, chemical works, industries and household solvents all have an effect on life. These pollutants are being released into, and trapped in the atmosphere in the form of 'acid rain'. Acid rain has an effect on the soil, it lowers its pH levels therefore the soil begins to leach minerals and trace elements necessary for plant nutrition. At very low pH levels, most valuable nutrients have leached away and "aluminium ions may appear in solution at poisonous concentrations", (Clegg & Mackean, 1998). Acid rain also has an impact on rivers and lakes, in that aluminium ions may reach poisonous concentrations resulting in fish ceasing to live in certain lakes and rivers. In order to prevent further pollution to our water systems, and to prioritise the components of our environment that we control, a classification system for water uses has been constructed and the water quality criteria for these uses has been formulated. (Mason, 1991). ...read more.

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