Quantcast CONCLUSIONS AND RECOMMENDATIONS - doerc230013

 

Order this information in Print

Order this information on CD-ROM

Download in PDF Format

     

Click here to make tpub.com your Home Page

Page Title: CONCLUSIONS AND RECOMMENDATIONS
Back | Up | Next

Click here for a printable version

Google


Web
www.tpub.com

Home


   
Information Categories
.... Administration
Advancement
Aerographer
Automotive
Aviation
Combat
Construction
Diving
Draftsman
Engineering
Electronics
Food and Cooking
Math
Medical
Music
Nuclear Fundamentals
Photography
Religion
USMC
   
Products
  Educational CD-ROM's
Printed Manuals
Downloadable Books
   

 

Share on Google+Share on FacebookShare on LinkedInShare on TwitterShare on DiggShare on Stumble Upon
Back
Figure 7. Relationship between 10- and 28-day survival and benthic community indices
Up
doerc23
Next
Figure 8. Biota to sediment accumulation factors (BSAFs) for PAHs in laboratory-exposed L. variegatus compared with BSAFs for field-collected oligochaetes
ERDC TN-DOER-C23
September 2001
Brunson et al. (1998) conducted a correlative type study designed, in part, to validate the use of the
oligochaete worm Lumbriculus variegatus as a bioaccumulation test species for freshwater sedi-
ments. Sediment samples and resident oligochaetes were collected from 13 navigational pools in
the Upper Mississippi and the St. Croix Rivers. Tissue residues were measured in L. variegatus
after 28 days of exposure to field-collected sediment and compared with tissue residues in
field-collected animals. While results of tissue analysis indicated that both PAHs and PCBs were
consistently found at concentrations above detection limits, the authors focused on the PAH data in
their evaluation of the 28-day L. variegatus bioaccumulation test. Lipid-normalized tissue concen-
trations of PAHs showed a positive correlation between laboratory-exposed and field-collected
organisms. Generally there was a change in tissue residue concentrations for individual PAHs; field
tissue residues were greater than laboratory tissue residues for the lower molecular weight PAH
tissue residues, and laboratory tissue residues were greater than field tissue residues for the high
molecular weight PAHs. The authors speculated that the observed differences between laboratory
and field-exposed animals may have been a result of any one of a number of factors. For example,
it is possible that the more water soluble lower molecular weight PAHs were lost during sampling
of sediments for the laboratory exposures. Differences may also have arisen from the spatial
heterogeneity of contaminants in the field (e.g., grab samples may have included sediment from
depths to which field-collected organisms were not exposed). Another possibility may be related
to the fact that field organisms may be exposed through a number of routes (e.g., sediment, water,
and food) whereas the primary route of exposure in laboratory bioaccumulation tests is through
direct contact and ingestion of sediment. There may also have been genetic/phenotypic or possibly
species differences between the lab and field organisms examined that may have lead to differences
in uptake. However, despite these differences, the authors indicate that the ratio of tissue concen-
trations for specific PAHs in laboratory and field-exposed organisms were generally similar
with about 90 percent of the corresponding concentrations for laboratory versus field-collected
organisms being within a factor of 2-3. In addition biota to sediment accumulation factors (BSAFs)
derived for lab and field data showed good correlation with the field-collected organisms, having
BSAF values equal to or higher than the laboratory (R2 = 0.80, p = 0.003). The good correlation
indicates that laboratory bioaccumulation tests with the oligochaete L. variegatus were good
predictors of bioavailability (Figure 8). Based on these findings the authors conclude, "Laboratory
results could be extrapolated to the field with a reasonable degree of certainty."
CONCLUSIONS AND RECOMMENDATIONS: Each of the two basic approaches employed
to date to field-validate laboratory bioassays (i.e., experimental/manipulative versus correlative/
observational) has inherent advantages and disadvantages. In general, correlative approaches are
subject to greater variability in the field portion of the assessment. In correlative studies, the spatial
variability of contaminants and contaminant mixtures remains intact. As one moves along the
"contaminant gradient," the type and amount of co-occurring contaminants change as do other
physical/chemical features of the sediment matrix and the biological communities that respond to
these factors. The difficulty in trying to ascribe differences in benthic community structure to
contaminant levels is evidenced by the low correlations found by Swartz et al. (1994) (Figure 4)
and McGee and Fisher (1999) (Figure 7). While spatial variability is inherent in environmental
contamination, such variability can confound attempts to validate responses measured in laboratory
tests where such variability is attenuated through homogenization of the sample matrix. The
experimental/manipulative approach attempts to overcome this variability via sample compositing
and/or homogenization to remove/reduce spatial variation.
13

Privacy Statement - Press Release - Copyright Information. - Contact Us - Support Integrated Publishing

Integrated Publishing, Inc.