DDT, Chlordane, Toxaphene and PCB Residues in Newport Bay and Watershed: Assessment of Hazard to Wildlife and Human Health - Reviews of Environmental Contamination and Toxicology - page 140

80

70

60

50

40

y = 359219e -0.0003x
R 2 = 0.5227

30

20

10

0

Jan-1979 Jan-1984 Jan-1989 Jan-1994 Jan-1999 Jan-2004

Date

Fig. 28 Chlordane concentrations in mussels from Newport Bay and Watershed. Data from
California Mussel Watch Program, 1980 -2000. The Mussel Watch Program was ended in 2000

Like red shiner data, mussel tissue data dating to 1980 from Newport Bay show
decreasing chlordane concentrations (Fig. 28 ). An exponential regression analysis
of mussel data (by wet weight) for the period of record (1980-2000) showed a
reasonably strong chlordane concentration decline rate in mussels (R 2 = 0.5227).
A split analysis was also performed on mussel data for the two periods 1980-1989 and
1990-2000. Although the split analysis indicated that neither the earlier (R 2 = 0.1176),
nor the later period (R 2 = 0.2968) demonstrate as statistically strong a decline as the
complete period, the entire mussel data set (1980-2000) refl ects a statistically signifi -
cant decline in chlordane tissue concentrations that is equivalent to a half-life for chlor-
dane of 6.2 years (decay rate of −0.00031 per day or −0.11 per year).

4.2 Benthic Triad Analysis of Impairment

The requirement for a TMDL for chlordane in Newport Bay is based on a triad assess-
ment of sediment chemistry, sediment toxicity to benthic organisms and degradation
of benthic communities. In this section, we examine the science underlying the triad
to determine whether the results indicate impairment to benthic organisms in Newport
Bay. The starting point is a discussion of the assays that make up the triad.
The sediment triad has three components. The fi rst component is the concentra-
tion of chlordane in sediments from Newport Bay. The SARWQCB staff report
contains data on chlordane levels in sediments from several reports (Appendix A-2
to SARWQCB 2006 ). Levels of chlordane in sediments from Newport Bay ranged
from <1 to 55 ppb in the time period 1994-2011 (see Fig. 25 above). The overall
average appears to be less than 10 ppb. As noted above, chlordane levels are declining
in the Watershed.