General

Definition of Bioaccumulation - http://www.iet.msu.edu/Tox_for_Public/bioaccum.htm

Bioaccumulation is an important process by which chemicals can affect living organisms. Bioaccumulation means an increase in the concentration of a chemical over time in a biological organism compared to the chemical's concentration in the environment. Compounds accumulate in living things any time they are taken up and stored faster than they are broken down (metabolized) or excreted.

The use of bivalves as biomonitors of various environmental contaminants has become common place over recent years with varying levels of success. In the United States the well publicised "Mussel Watch Program" (e.g. San Francisco http://www.sfei.org/rmp/1997/c0501.htm) has produced an enormous amount of biomonitoring information concerning the mussel Mytilus.

In NSW the Environment Protection Authority has used this technique to monitor the effects of the three Sydney Deepwater Ocean Outfalls with some success (Department of Environment and Heritage site http://www.deh.gov.au/coasts/publications/somer/annex2/philip.html#philip94). Oysters are one component of this monitoring program which also involves fish, benthic communities and sediment analysis. Biomonitoring utilising oysters has also been the focus of a number of research programs undertaken by universities.

Biomonitors present some major advantages over the normal analysis of pollutants in the water column. Pollutants are concentrated in the oysters tissues which makes the detection of the metals a simpler task when compared to the generally low levels found in the water, even in contaminated environments. The metals are accumulated through time giving a time averaged result as opposed to the sampling of waters which are extremely variable through time. The use of oysters in a monitoring program is far more cost effective and provides results which can be confidently interpreted. Finally pollutant levels in tissues will give some indication as to the potential levels in other biota in the area and thus an idea as to the potential hazards of the consumption of these animals and plants by humans and the possible toxicological effects on the organisms themselves.

Drawbacks to the use of this type of biomonitor are that few have been adequately "calibrated" and the methodology for their deployment and analysis has not been properly researched. Calibrated in this instance means to gain an understanding of how the indicator organism deals with environmental levels of the contaminant through time, i.e. does it accumulate it to a certain level then regulate it at that level or does it just accumulate the contaminant until it dies or any of a number of possible scenarios. Another question is over what period of time does the potential accumulation/depuration take place? This question seems to have been addressed by the EPA with 3 months being the proposed deployment period for Sydney Rock Oysters.

Protocol

Example using the Sydney Rock Oyster (S. commercialis)

• Large/old (4-5 years) oysters are utilized and sourced from an area of low pollutant background.
• Oysters are then placed in commercially available plastic oyster trays for deployment in the field.
• Prior to deployment, oysters are cleaned of all encrusting growth and sediments using a wire brush in fresh water.
• They were then dried in air, measured with vernier calipers (length, depth and breadth).
• Plastic mesh (10 mm square) is attached to the top of the tray using cable ties to prevent oyster loss due to predation or wave action.
• No more than 48 hours should pass between preparation and deployment.
• Prior to deployment a selection of individuals from the original sample population should be analysed for background levels.
• Oysters can be deployed intertidally on normal piles and rails or subtidally and fixed to the benthos.
• An appropriate experimental design should be applied to the selection of impacted and reference sites.
• The deployment period should be for approximately 3 months.
• Upon retrieval oysters should be frozen whole pending analysis. The analysis of 3 subsamples from a homogenate of 50 individuals has been shown to give a reasonable indication of the variability within a sample population.

Cost

13 metals per oyster tissue analysis = $120.00 approximately

Example program
3 impacted sites and 3 reference sites with triplicate within site replication = $15,000 (materials only)

Case Studies

Copper in Sydney Rock Oysters – Queensland University
http://www.coastal.crc.org.au/postgraduates/presentations/russell_richards.pdf
Zebra Mussels as bioaccumulators
http://www.wes.army.mil/el/zebra/zmis/zmishelp/bioaccumulation.htm
US Geologic Survey
Striped Bas as bioaccumulators of PAHs and organochlorines
http://sfbay.wr.usgs.gov/access/WP-BioStud1.html
Sydney Water Environmental Indicators Monitoring report
http://www.sydneywater.com.au/html/environment/eicr/pdfs/eimpr.pdf

Person Contact

Associate Professor Ken Brown
Department of Environmental Sciences
University of Technology, Sydney
P.O. Box 123, Broadway
NSW. Australia. 2007
Office: Rm G.03 (St Leonard’s Campus)
Phone: +61 2 9514 4042
Fax: +61 2 9514 4079
E-mail: Kenneth.Brown@uts.edu.au

Organisation Contact

NSW Environment Protection Authority
http://www.epa.nsw.gov.au/home.htm

Advanced Reference