10
P. Tett
Whereas azamethiphos and emamectin are solely of human manufacture, and
hence were never present in ecosystems before humans introduced them, the story
about antifouling compounds is more complex (Readman 2005). These compounds
are used to prevent the growth of bacterial slime and seaweed sporelings on nets
and supporting structures. TBT, which did this effectively, was entirely synthetic,
but is now banned. Modern paints and steeping liquids use compounds of copper, and
sometimes zinc, which dissolve slowly in seawater, releasing ions of copper
and zinc. It is these ions that are harmful to micro-organisms that might settle and
grow on the netting or cage. Paradoxically, copper and zinc are needed in small
amounts by living creatures, being essential for some biochemical reactions, and
are toxic only at higher concentrations. So the challenge for the designers of antifouling materials is to ensure that they release sufficient copper etc to kill bacteria
and algal spores close to the surfaces they are intended to protect, but without dissolving too quickly, which would increase the risk of wider harm and would require
more frequent treatments.
Consequently, some manufacturers add “booster biocides” to augment the antifouling action. These include the synthetic chemical, copper pyrithione. However,
research suggests that when zinc is present, the pyrithione part can swop from copper to zinc, resulting in zinc pyrithione. This compound, used in anti-dandruff
shampoos and as a fungicidal additive for plastics, has been found to be highly
toxic to copepods as well as planktonic micro-algae (Hjorth et al. 2006; Maraldo
and Dahllöf 2004).
The last part of this story is that farmed fish need copper, and so it is added to
their food, perhaps in unnecessarily large amounts that the fish excrete into the
water or by way of their faeces; because of the latter, the seabed beneath fish cages
may contain high levels of copper, which dissolves to increase the concentration of
copper ions in the sediment pore waters, and which may diffuse back into the water
column.
1.5 DPSIR and EQS
The DPSIR system breaks the ecosystem effects of pollutants into 5 steps. In this
acronym, D stands for driver, P for pressure, S for state, I for impact, and R for
response. The state is that of the ecosystem under consideration; the pressures
are those generated by human activity whose change provides the drivers. Thus
the growth of salmon-farming is the driver that has led to increasing loading of
Scottish fjords with farm waste, with consequential pressures on the fjordic ecosystems from organic matter, mineral nutrients, and chemicals. A build-up of
particulate waste beneath a fish cage, with consequent death of larger sea-bed
animals, exemplifies a highly visible impact, and the response to this impact has
been for society to impose more stringent conditions on the location and management
of fish farms.
P. Tett
Whereas azamethiphos and emamectin are solely of human manufacture, and
hence were never present in ecosystems before humans introduced them, the story
about antifouling compounds is more complex (Readman 2005). These compounds
are used to prevent the growth of bacterial slime and seaweed sporelings on nets
and supporting structures. TBT, which did this effectively, was entirely synthetic,
but is now banned. Modern paints and steeping liquids use compounds of copper, and
sometimes zinc, which dissolve slowly in seawater, releasing ions of copper
and zinc. It is these ions that are harmful to micro-organisms that might settle and
grow on the netting or cage. Paradoxically, copper and zinc are needed in small
amounts by living creatures, being essential for some biochemical reactions, and
are toxic only at higher concentrations. So the challenge for the designers of antifouling materials is to ensure that they release sufficient copper etc to kill bacteria
and algal spores close to the surfaces they are intended to protect, but without dissolving too quickly, which would increase the risk of wider harm and would require
more frequent treatments.
Consequently, some manufacturers add “booster biocides” to augment the antifouling action. These include the synthetic chemical, copper pyrithione. However,
research suggests that when zinc is present, the pyrithione part can swop from copper to zinc, resulting in zinc pyrithione. This compound, used in anti-dandruff
shampoos and as a fungicidal additive for plastics, has been found to be highly
toxic to copepods as well as planktonic micro-algae (Hjorth et al. 2006; Maraldo
and Dahllöf 2004).
The last part of this story is that farmed fish need copper, and so it is added to
their food, perhaps in unnecessarily large amounts that the fish excrete into the
water or by way of their faeces; because of the latter, the seabed beneath fish cages
may contain high levels of copper, which dissolves to increase the concentration of
copper ions in the sediment pore waters, and which may diffuse back into the water
column.
1.5 DPSIR and EQS
The DPSIR system breaks the ecosystem effects of pollutants into 5 steps. In this
acronym, D stands for driver, P for pressure, S for state, I for impact, and R for
response. The state is that of the ecosystem under consideration; the pressures
are those generated by human activity whose change provides the drivers. Thus
the growth of salmon-farming is the driver that has led to increasing loading of
Scottish fjords with farm waste, with consequential pressures on the fjordic ecosystems from organic matter, mineral nutrients, and chemicals. A build-up of
particulate waste beneath a fish cage, with consequent death of larger sea-bed
animals, exemplifies a highly visible impact, and the response to this impact has
been for society to impose more stringent conditions on the location and management
of fish farms.