Chemistry and behaviour: a balancing act October-November 2009 Journal
|Leslie Saunders is seen in the field collecting sediments and snails, then Stephen Marklevitz and Peter Walker are seen going up the steps from the beach to the van and are also seen in the fish lab placing sediment in tanks to maintain the animals. Daniel Beach and Leslie are performing some of the chemical analyses in the laboratory. These students were or are enrolled at Dalhousie University as undergraduate or graduate students in the Environmental Programme (LS), Marine Biology/Oceanography (SM), Chemistry (DB) and Microbiology/Immunology (PW).|
Since a picture is worth a thousand words, this one is intended as a short story. The photo collage briefly captures the steps behind our development of tools to assess the state of a marine environment. We are interested in the answer to the “so what?” question behind detecting contaminants in sediments. Our work focused on understanding the meaning behind the presence of priority pollutants, polycyclic aromatic hydrocarbons (PAH) deriving from combustion and fossil fuels. These chemicals are hydrophobic and bind to organic rich particles. Levels of PAH have been shown to increase near shore in the proximity of urbanisation and to be related to, in major part, increased traffic.
Our group developed tests to examine how amphipods residing in sediments react when faced with two choices: sediment obtained from their native location and one being questioned because of the chemical content. After working for many summers to ascertain the validity of our discoveries, it was demonstrated that in the case of 5 out of 7 samples, animals will avoid harbour sediment containing PAH at levels similar to those labelled as “probable effects levels” (PEL) by the Canadian Council of Ministers of the Environment. This PEL refers to a 50% probability of developing a toxic response. The bioavailability of the PAH was further determined by analysing the PAH body burden of the amphipods. The level detected in tissue extracts was 1,000 times lower than levels associated with LC50 (lethal concentration to 50% of a population). This is the standard used to readily determine toxicity.
Our group also examined the response of mud snails to the presence of two sediments overlaid with seawater, or to just one overlaid with seawater. The response of snails to stress involves multiple steps. Not only can they escape from sediment by going to the water layer, they can also go to the glass surface of the tank. If they are still experiencing exposure, over time they will flip over from being on their foot to lying on their shell with the soft tissue extended, and then later on to being enclosed within the shell. However, unlike the mud shrimp which can only accumulate the PAH, the snails can also transform it. We are now trying to link the fate of the chemical in tissue extracts to the observed behaviour. This would enable us to predict and ultimately to prevent, further deleterious effects.
The sediment area tested for toxicity was previously linked to the bioaccessibility of contaminants to mussels and numerous ensuing levels of toxicity going from the molecular to the population level. The choice of benthic invertebrates is linked to enhancing the outcomes of three pronged studies where contaminants are analysed in sediments, LC50 are determined using various species and the abundance and variety of benthic inhabitants is determined. The above tool would permit a scientist to establish a cause and effect relationship between chemicals and effects. Therefore it would offer an ability to remedy the state of a site, as deemed necessary.