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

State of Saldanha Bay & Langebaan Lagoon 2011
Sediments
5.4.1 Historical data
Dramatic increases in trace metal concentrations, especially those of cadmium and lead
after the start of the iron ore export from Saldanha Bay, raised concern for the safety and health of
marine organisms, specifically those being farmed for human consumption (mussels and oysters). Of
particular concern were the concentrations of cadmium which exceeded the lower toxic effect level
published by the NOAA. Both lead and copper concentrates are exported from Saldanha Bay and it
was hypothesised that the overall increase of metal concentrations was directly associated with the
export of these metals. The concentrations of twelve different metals have been evaluated on
various occasions in Saldanha Bay; however, the overall fluctuations in concentrations are similarly
reflected by several key metals throughout the time period. For the purposes of this report, four
metals that have the greatest potential impact on the environment were selected from the group.
These are cadmium (Cd), lead (Pb), copper (Cu) and nickel (Ni).
The earliest data on metal concentrations in Saldanha Bay were collected in 1980, prior to
the time at which iron ore concentrate was first exported from the ore terminal. The sites sampled
were 2 km north of the Multi-purpose Quay (Small Bay) and 3 km south of the Multi-purpose Quay
(Big Bay) and metals reported on included lead (Pb), cadmium (Cd) and copper (Cu). Concentrations
of these metals in 1980 were very low, well below the sediment toxicity thresholds (Figure 5.21,
Figure 5.25, Figure 5.23 and Figure 5.27). Subsequent sampling of metals in Saldanha Bay (for which
data is available) only took place nearly 20 years later in 1999. During the period between these
sampling events, a considerable volume of ore had been exported from the Bay, areas of Saldanha
Bay had been dredged (1997/98), and the Mussel Farm and the small craft harbour (Yacht Club
Basin) had been established (1984). As a result of these activities, the concentrations of metals in
1999 were very much higher (up to 60 fold higher) at all stations monitored (Figure 5.21, Figure 5.25,
Figure 5.23 and Figure 5.27). This reflects the accumulation of metals in the intervening 20 years,
much of which had recently been re-suspended during the dredging event and had settled in the
surficial (surface) sediments in the Bay. Concentrations of most metals in Saldanha Bay were
considerably lower in the period 2000-2010, although nowhere near levels measured in 1980. This
closely mirrors changes in the proportion of mud in the sediments, and most likely reflects the
removal of fine sediments together with the trace metal contaminants from the Bay, by wave and
tidal action. Monitoring surveys between 2001 and 2011, revealed that with a few exceptions, metal
concentrations had continued to decrease in Saldanha Bay and were much reduced from the
exceptionally high concentrations recorded in 1999 and 2000.
5.4.2 Analysis and results for 2011
Sediments were analyzed for concentrations of aluminium (Al), iron (Fe), copper (Cu),
cadmium (Cd), nickel (Ni), lead (Pb) and zinc (Zn). For the purpose of this report only the data for Cd,
Cu, Pb, Ni and Fe are presented as these are the metals deemed to pose the greatest threat to the
health of the marine environment. Metals in the sediments were analyzed by Scientific Services
using a Nitric Acid (HNO 3 ) / Perchloric Acid (HClO 3 )/ Hydrogen Peroxide (H 2 O 2 )/ Microwave digestion
and JY Ultima Inductively Coupled Plasma Optical Emission Spectrometer. The concentrations of
metals in the sediments of Saldanha Bay and Langebaan Lagoon in 2011 are shown in Table 5.3. The
concentrations of trace metals at the sites sampled in 2011 were used to interpolate the metal
concentrations over the full extent of the Bay and Lagoon using GIS software. These interpolations
provide an indication of the spatial variation in the concentration of the various trace metals in the
Bay and the Lagoon.
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