Sediment Effects Range Median Quotient (Long and MacDonald, 1998) 
ERM-Q — The average quotient of the measured concentration of a defined list of 
contaminants divided by their ERM values. 
The ERM-Q index attempts to summarize the overall contaminant exposure 
resulting from a mixture of contaminants by dividing the measured sediment 
concentration of a contaminant by its ERM value, followed by taking an average value 
of these quotients. Average ERM-Q values for samples from California and San 
Francisco Bay were approximately two times higher than those for sites in Washington 
and Oregon (Fig.3.2.5). Thompson and Lowe (2004) have suggested that an average 
ERM-Q of <0.146 was a reasonable guideline for reference condition with regard to 
sediment contamination in the San Francisco Estuary. For a national data set, Long et 
al. (1998) suggested that values <0.1 indicate a low probability (11.6%) of having highly 
toxic sediments. All values of average ERM-Q for the five areas in the present study 
(Fig.3.2.5) are below these guidelines. 
a 
o: 
LU 
0.14 - 
0.12 - 
0.10 - 
0.08 - 
0.06 - 
0.04 - 
0.02 - 
0.00 - 
WEST WA OR CA SF BAY 
Figure 3.2.5. Average Effects Range-Median Quotient (ERM-Q) values for sediment 
contaminant concentrations for intertidal samples obtained in 2002 for the West Coast 
region, individual states, and San Francisco Bay (mean ± 1 sd). 
31 
