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

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State of Saldanha Bay & Langebaan Lagoon 2011 Sediments 5.4.2.3 Lead There has been a widespread elevation of lead (Pb) concentrations in the environment due to mining, smelting and the industrial use of Pb (OSPAR 2010). Pb is a persistent compound which is toxic aquatic organism and mammals, and thus the contamination is of concern for the marine environment and human consumption (OSPAR 2010). Pb was detected at all sites in Saldanha- Langebaan, with the exception of three sites in the lagoon and two in Big Bay. The concentration of lead at site SB 14 (Multi-purpose Quay) exceeded the ERL value in 2011 (Figure 5.24 and Table 5.3). Other sites with high concentrations included the Yacht Club Basin, Donkergat and Salamander Bay (Figure 5.24 and Table 5.3). The normalized Pb:Al ratios were highest at sites SB3 (north end of the channel), SB14 (multi-purpose quay), SB42 (close proximity to multi-purpose quay), D1 (Donkergat) and S1 (Salamander Bay), suggesting anthropogenic input at these points (Figure 5.19). The normalized Pb:Al ratios were also elevated at SB3 and SB14 in 2008 and 2009. The high PB concentrations and Pb:Al ratios in close proximity to the multi-purpose quay and landward (SB3) are most likely attributable to the export activities that take place in this area. The high PB concentrations and Pb:Al ratios at Donkergat and Salamander Bay are in all likelihood attributable to the dredging activities that took place in the area in 2009/10. Pb concentrations are 29 and 80 times higher at the Yacht Club Basin and at the multipurpose quay compared to 1980 concentrations respectively (Table 5.4). Elevated Pb along the multi-purpose quay can be attributed to the export of lead ore, storm water runoff and the discharge of ballast water (in which Pb concentrations are higher than guideline limits). Furthermore, both sites are depositional zones which have lead to the long-term accumulation of Pb in these areas. The temporal variations in the concentration of Pb in Saldanha Bay sediments can be seen in Figure 5.25. In 1980, the concentrations of lead in the sediments were very low at all sites (~0.8 mg/kg), but increased notably at all sites after the 1997 dredge event. In 1999 the concentrations of lead at the Yacht Club Basin and Mussel Farm exceeded the lower threshold value set by NOAA at which toxic effects are likely to be observed in sensitive species (ERL = 46.7 mg/kg). Concentrations of Pb at the Multi-purpose quay exceeded the ERL value in 2000 and again in 2008 and 2009. The sediments from all sites within Small Bay (except the end of the ore terminal) showed an increase in lead concentrations in 2008. This is concerning given that there was an apparent decline in Pb concentrations at these sites between 1999/2000-2004. This increase in Pb in the sediments may be linked to the maintenance dredging that took place at the multipurpose quay and Mossgas Quay at the end of 2007/beginning of 2008 (see §3.3.1). The concentration of Pb decreased again at all sites within Small Bay except the Multi-purpose Quay and the Channel End of the Ore Terminal in 2009. Subsequent samples taken in 2010 revealed that Pb concentrations had declined further at all sites with the exception of the Yacht Club Basin, which increased very slightly. Pb concentrations at all sites fell below the ERL in 2010, suggesting some recovery of the system since the 2007/2008 dredge event. The 2011 survey revealed that Pb concentrations at all sites within Small Bay increased between 2010 and 2011 and decreased at the majority of sites in Big Bay and Langebaan Lagoon. This result is concerning given that the mud fraction in the sediments decreased over the same time period. This suggests that Pb inputs into Small Bay exceeded the rate at which the area is being flushed. The sites where Pb concentrations are most concerning are those around the multi-purpose quay where concentration greatly exceeded ERL levels. 114 ANCHOR e n v i r o n m en t a l
State of Saldanha Bay & Langebaan Lagoon 2011 Sediments Figure 5.24. Variation in the concentration of Lead (Pb) in the sediments in Saldanha Bay and Langebaan Lagoon as revealed by the 2011 survey results. 115 ANCHOR e n v i r o n m en t a l
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