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Short Term Studies of Water Soluble Fractions of Diesel on Growth of Chaetoceros calcitrans

Dola Bhattecharjee and Olivia J. FernandoCenter of Advanced Study in Marine Biology, Annamalai University, Parangipettai 608502, Tamil Nadu, India

Arloe Fontenot

October 31, 2008

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Introduction and BackgroundCoastal Areas are fragile ecosystems susceptible to addition of both stable and biodegradable compounds from land.

Coastal areas and shorelines are also highly affected by marine oil spills.

A lot of research has been done on the fate of Petroleum Hydrocarbons (PHCs) in the marine environment.

PHCs come from oil (petroleum) and its refined products; one of those products is diesel.

Since oil and its products tend to be less dense than water, surface dwelling populations of microalgae and other microorganisms are often the most obvious victims of oil spills.

Toxicity of these hydrocarbons depends on their concentration and type; exposure time; state; prevailing environmental conditions, and sensitivity of affected species.

Effects of these contaminants can be determined by growth measurements.

Algae is frequently assayed due to its role in the food web, and decreases in algal density and species reduces the marine environment’s primary products and biodiversity.

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Previous Research- Many studies have reported reduction in photosynthesis and changes in microalgal growth

properties (Lee and Takahashi, 1977).

- Bioaccumulation of PHCs in benthic diatoms has been observed from oil-contaminated sites (Thompson and Eglintan, 1979).

- Also, oil has been responsible for accumulation and production of different metabolites in blue-green algae (Prouse 1976, Corniglia 1980).

- Macroalgae experienced reduced photosynthesis when exposed to high concentrations of oil; whereas Microalgae experienced a photosynthetic enhancement at low oil exposure concentrations (Shields 1973, Prouse 1976).

- Diesel considered a major use PHC.

- Diesel’s toxic effects were observed to be several times higher than crude, when tested against Tetraselmis gracilis, a green flagellate (Phatarpekar and Ansari, 2000).

- High Morality was reported among benthic crustaceans and benthic algae blooms in diesel contaminated salt marsh sediments (Carmen, 2000).

- Isochrysis galbana, a unicellular golden-brown algae, has also been studied for bioavailability of naphthalene (Wolfe, 1998).

- Carmen, in 1997, did report a diesel-attributed increase in microalgal biomass.

This was thought to be attributed to reduced meofaunal grazing.

- Nalco PHCs were also compared on meofauna by Roseth in 1996.

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Study Objective

- This study aimed to investigate suppressive growth effects of various water soluble fractions (WSFs) of diesel on Chaetoceros calcitrans.

- Chaetoceros calcitrans falls under genus Chaetoceros, the largest genus of marine planktonic diatoms with approximately 400 species)

- Toxicity was determined by EC50 (mean effective concentration) at the end of 96hours.

- A good example of Chaetoceros

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Materials and Methods

     

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Materials and Methods

                              

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Results

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Results

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Results and Discussion- EC50 of WSF of diesel oil is around 75-78% after 96hrs- So, a diesel oil concentration of approximately 36.56-38.02 mg/L is the

96hr EC50, determined through graphical interpolation.- Water soluble fractions did not appear toxic from 5-40%, and a slight

stimulation was observed as before (Soto, 1975)- Growth suppression was observed at greater than 40% and well over

80%.- Two types of toxic effects on algae:

-Effects from organism coating (reducing CO2 diffusion and light penetration).-Effects from organism uptake and disruption of cellular metabolism (low MW lipophilic aromatics can easily penetrate the cells).

- Aromatic hydrocarbons are more water soluble and tend to persist longer than alkanes of similar MW.

- Exposure to these aromatics can prolong the cellular lag phase.- Furthermore chemical modifications of PHCs also increase toxicity.- These are the main factors contributing to diesel oil

toxicity!

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Conclusion- Incorporation of Oxygen makes aromatic compounds more water soluble

and causing retention in solution.- The subsequent polar, non-polar mixtures become more readily

concentrated in cells causing damage to cell membranes, ultimately leading to cell death.

- Hydrocarbons are by and large more toxic to microalgae than to animals.

And Finally- Although not terribly detrimental to coastal microalgae populations,

better handling procedures need to be put into practice regarding the loading, unloading, dumping, and general handling of diesel oil, especially in or near vulnerable coastal waters.

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