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DOLORS PLANAS & STÉPHANIE HAMELIN'S
INTERVIEW
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DOLORS PLANAS

When I arrived in Quebec, quite a few years ago, I found that this was a paradise. In the summer there were so many birds, so many animals. It really was a paradise. But eventually we realized that this paradise, all the plants, and the algae on the plants, known as biofilm, contain contaminants derived from human actions, which could be hazardous for animal and plant life because they were being contaminants derived from human actions were being transported throughout the biosphere. Our interest began from there. We asked ourselves: Could all the food we see here for fish, birds, muskrats and other animals living in the water actually be poisoning them? This question spurred us to take a closer look. What was happening on the level of these masses of plants and associated algae, that attracted so many birds and other animals during the summer? That’s why we started studying one of the contaminants we knew was present in Lake Saint-Pierre: mercury. Because we had previously worked on Lake Saint-François, before we started working on Lake Saint-Pierre in the 2000s, we knew that aquatic plants and algae can accumulate many contaminants. In the case of Lake Saint-François, we found high levels of PCBs, organic contaminants associated with industries in the Cornwall area and the United States. We wanted to find out whether, as we found with PCBs, plants can accumulate contaminants dissolved in the water and also contaminants in the sediments because, like trees or the grass in our gardens, aquatic plants have roots. And those roots can absorb contaminants from the sediments. Another question is: all the mercury that has previously entered Lake Saint-Pierre... Is it pumped out of the water and absorbed by plants? Another question we asked was: is the algae associated with plants capable of transforming mercury, mercury in its mineral form, into toxic mercury – what we call methylmercury? The algae is capable of transforming mineral mercury into methylmercury. This is the question that led us to work on Lake Saint-Pierre. I have three graduate students - one master’s student and two doctoral students - who have studied this issue, the accumulation of mercury in plants and in the algae growing on those plants, and the transformation of that mercury into its toxic form, methylmercury. When herbivores eat the plants or the algae, they will also...the mercury will be passed on to them. And every time this happens, every time one animal eats another, not only does mercury pass from one trophic level to another, but its concentration increases. Let’s say a plant has one gram of mercury, okay, then these animals - herbivores, snails, the little shrimps we sometimes see among the plants - they eat the algae and aquatic plants. Their level of mercury will increase because they consume it and do not eliminate it. Mercury concentrations can increase up to 5,000 times over the lifespan of a small herbivore. Afterwards, if these small herbivores are eaten by a Yellow Perch, then the mercury concentration in the perch compared to the snails and shrimps it has eaten will be another 1,000 to 10,000 times higher. Once you get to the level of predatory fish like Walleye and Northern Pike they accumulate so much mercury that it really is as if they have been poisoned with high doses of mercury. And if humans eat them, they can have very strong toxic effects.

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STÉPHANIE HAMELIN

This poster shows the results of the doctoral thesis I am doing under the direction of Dolors Planas, who is here at UQAM, and Marc Amyot, my co-director at Université de Montréal. What I was interested in was to investigate. We talk about aquatic plants as food for other links in the food chain of Lake Saint-Pierre. We want to find out whether or not these plants and algae are contaminated with mercury. And which ones are the most contaminated. The first thing I did was to go sampling. Here we can see some aquatic plants. I also sampled the biofilm, the layer of algae growing on aquatic plants. I tried to find out what level of mercury was present. To give you an example, this figure shows mercury concentrations. This large bar represents the biofilm and the small bar is the large aquatic plant. So you can see that if you compare...We always compare them as a pair. So, this is the biofilm and this is the aquatic plant. We always find around ten times more mercury in the biofilm than in the plant itself. So, as far as contaminants are concerned, for an organism who is eating vegetation, it’s more "dangerous" to eat the biofilm than to eat the plant. Biofilm is the green scum that grows on aquatic plants. It’s also called periphyton. You may have heard this term. It’s a matrix composed mainly of algae but it also contains microbes, fungi and detritus. You often see it when you walk in small streams. You can see a bit of green "moss" on the rocks. In fact, the moss is an algal biofilm. We see the same thing on aquatic plants in Lake Saint-Pierre. It’s natural. It’s even good for an ecosystem to have some because it is the foundation of the food chain. If there was no biofilm, there wouldn’t be enough food in the lake. Some insects specialize in eating only biofilm. Other insects specialize in eating only plants. I am talking about insects now because they occupy the next highest level of the food chain, known as the benthos. At the next level are fish, which eat the benthos. Generally, mercury concentrations are higher in early summer: May, June, July; later in the year they stabilize a little. The station where I found the most mercury is shown in orange. This is the Giraudeau station, here on the north shore. The higher concentrations are probably linked to nutrient loads, but also to the fact that the water is more acidic. Mercury may thus be more readily available for absorption by plants and algae. What’s interesting is that mercury is one thing but there are several forms of mercury. One of the most toxic forms is methylmercury. It is transformed from ionic mercury (the form found in the air) to methylmercury, an organic mercury that is more toxic, which then bioaccumulates and bioamplifies. I wanted to see what proportion of this more toxic mercury I could find in the plants I was sampling. We observed that methylmercury is present in much greater amounts at the BSF Baie Saint-François station, here on the south shore. So the most highly toxic mercury is found here. Why? Because there are high nutrient loads from agriculture, phosphorus and nitrogen, that fertilize plants and algae. This causes them to proliferate. They become more metabolically active, and can more easily transform mercury to a more toxic form. This is a poster by William, a master’s student of Dolors who has now completed his studies. He used data on mercury and methylmercury from my doctoral thesis and the analyses I carried out. He tried to extrapolate the data to the scale of Lake Saint-Pierre to determine, based on plant biomass, how mercury might be distributed within the lake. Basically, these are the results of his research. As you can see on this map, the redder areas are the places where we found more mercury. Mercury concentrations are mainly linked to plant biomass, which is much greater in these areas.