State of the Bay Report 2011-Final.pdf - Anchor Environmental

State of Saldanha Bay & Langebaan Lagoon 2011
Sediments
iron are commonly used as normalizes for trace metal content as they ubiquitously coat all
sediments and occur in proportion to the surface area of the sediment (Gibbs 1994); they are
abundant in the earth’s crust and are not likely to have a significant anthropogenic source (Gibbs
1994, Summers et al. 1996); and ratios of metal concentrations to Al or Fe concentrations are
relatively constant in the earth’s crust (Summers et al. 1996). Normalized metal/aluminium ratios
can be used to estimate the extent of metal contamination within the marine environment, and to
assess whether there has been enrichment of metals from anthropogenic activities. In this study
metal concentrations were normalized against (divided by) aluminium and not iron due to the
known anthropogenic input of iron from the iron ore quay and industrial activity in Saldanha Bay.
Figure 5.19. Metal:Al ratios for Copper, Lead, Cadmium and Nickel for sediments sampled in 2011 from
Saldanha Bay-Small Bay (SB), Big Bay (BB), Langebaan Lagoon (LL), Donkergat (D) and
Salamander Bay (S)
Metal enrichment factors were calculated for Cd, Pb and Cu relative to the 1980 sediments
(Table 5.4). Unfortunately historic enrichment factors could not be calculated for Ni as no data was
available for this metal in 1980. Enrichment factors equal to (or less than) 1 indicate no elevation
relative to pre-development sediments, while enrichment factors greater that 1 indicate a degree of
metal enrichment within the sediments over time. Enrichment factors were not calculated for
Langebaan Lagoon since all concentrations were below the detection limits.
5.4.2.1 Cadmium
Cadmium (Cd) is a trace metal used in electroplating, in pigment for paints, in dyes and in
photographical process. The likely sources of Cd to the marine environment are in emissions from
industrial combustion process, from metallurgical industries, from road transport and waste streams
(OSPAR 2010). A likely point source for Cd contamination in the marine environment is that of
stormwater drains. Cd is toxic and liable to bioaccumulation, and is thus a concern for both the
marine environment and human consumption (OSPAR 2010). The Cd concentrations detected in
2011 exceeded the ERL prescribed by NOAA at the Yacht Club Basin and at the multi-purpose quay
(Figure 5.20 and Table 5.3). Both areas had a relatively high mud content which suggests that these
areas are subject to high retention rates. The normalized Cd:Al ratios were high at the Yacht Club
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