The uptake of contaminants by marine organisms occurs through ingestion of food
and detrital particles, water exchange at feeding and respiratory surfaces, and
adsorption of chemicals onto body surfaces. These contaminants may be stored in
skeletal material, shells, and soft tissues. Biological monitoring has been a component
of the County’s routine monitoring programs for many years, to monitor contaminants
that may be bioaccumulated by shellfish.
Prior to 1996, shellfish samples were collected from a number of clam species,
whichever species were present at the time of collection. Since this type of sampling
could not facilitate trend analysis, a single species was chosen for monitoring. From
1996 to the present, shellfish samples have been comprised of a single species of
butter clam, Saxidomus giganteus. Shellfish samples were collected once a year, in August,
up until 2006. At that time, the shellfish monitoring program was increased to twice-yearly
sampling, in March and August, to assess seasonal variabilities in tissue chemical concentrations.
Up until 2006, shellfish tissue samples were analyzed for metals and trace organic
compounds. These measurements provide an indication of potential health risks to
both shellfish and humans that consume them. Organic compounds were rarely detected
in shellfish tissues, however, and were thus discontinued as part of the shellfish
monitoring program. Metal concentrations continue to be monitored in shellfish tissues.
Percent lipids in shellfish are also monitored as this parameter provides an indication
as to the seasonal state of the organism. In 2008, the analysis of 14 polybrominated
diphenyl ether congeners (PBDEs) was added to the shellfish monitoring program.
PBDEs were added to the shellfish suite of analytes due to their high detection
rate in sediments and their status as an emerging chemical of concern with potential
bioaccumulative properties. Analysis of PBDEs in shellfish tissue provided a useful
data set in 2008 and this analysis is continuing in 2009.
Download the analytical protocol matrix.
Shellfish tissue samples will be collected twice in 2009, in March and August, from
nine intertidal monitoring stations. Five outfall-vicinity monitoring stations will
be located inshore of the West Point (two stations) and Vashon treatment plant outfalls
and the Alki and Carkeek CSO treatment plant outfalls. Four ambient shellfish monitoring
stations will be located at Edwards Point, Point Wells, Golden Gardens Park, and
Normandy Park. Analytes will include trace metals, percent solids, percent lipids,
and polybrominated diphenyl ethers (PBDEs).
Data for the routine shellfish monitoring program are not currently available for
download through the web site. Please contact
with any data requests.