Heavy metal pollution in Wellington Harbour

New Zealand Journal of Marine and Freshwater Research

ISSN: 0028-8330 (Print) 1175-8805 (Online) Journal homepage: http://www.tandfonline.com/loi/tnzm20

Heavy metal pollution in Wellington Harbour P. Stoffers , G. P. Glasby , C. J. Wilson , K. R. Davis & P. Walter To cite this article: P. Stoffers , G. P. Glasby , C. J. Wilson , K. R. Davis & P. Walter (1986) Heavy metal pollution in Wellington Harbour, New Zealand Journal of Marine and Freshwater Research, 20:3, 495-512, DOI: 10.1080/00288330.1986.9516169 To link to this article: http://dx.doi.org/10.1080/00288330.1986.9516169

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New Zealand Journal of Marine and Freshwater Research, 1986, Vol. 20: 495-512 0028-8330/86/2003-0495$2.50/0 © Crown copyright 1986

495

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Heavy metal pollution in Wellington Harbour

P. STOFFERS1 G. P. GLASBY2 C. J. WILSON3 K. R. DAVIS1 P. WALTER1 1 Institut für Sedimentforschung Universität Heidelberg Postfach 10 30 20 D-6900 Heidelberg Federal Republic of Germany 2 New Zealand Oceanographic Institute Department of Scientific and Industrial Research Private Bag, Kilbirnie Wellington New Zealand 3 Wellington Regional Council P. O. Box 27-242, Wellington New Zealand Abstract Heavy metal analysis of the < 20 µm fraction of marine sediments from Wellington Harbour and Waiwhetu Stream have shown that the Waiwhetu Stream is easily the most polluted area in the Wellington Harbour system with Pb and Zn in the extremely polluted category and Cu, Cd, and Hg in the moderately to strongly polluted category. These elements have different distributions in the stream sediments reflecting their different sources from adjacent factories. In Wellington Harbour itself, the central basin of the harbour suffers from minimal pollution. Pb, and to a lesser extent Zn and Cu, are the main pollutants and local enrichment of these elements is noted in Lambton Harbour basin, off Pencarrow and Moa Point outfalls, in Evans Bay, and off Petone and Kaiwharawhara. The geochemical data do not enable us to identify the source of the pollutants unambiguously. A summary of the history of waste discharges into the harbour suggests that heavy metal pollution may have been higher in the past. Keywords heavy metals; pollution; Wellington Harbour; New Zealand; lead; zinc; copper; cadmium; mercury Received 6 March 1985; accepted 2 December 1985

INTRODUCTION One of the unfortunate side effects of industralisation is the discharge of heavy metals into the environment and it is now accepted that the study of the heavy metal distribution in the associated sediments is a useful way to monitor the input of such pollutants (Suess 1978; Forstner & Wittman 1981; Forstner 1983; Salomons & Forstner 1984; Santschi et al. 1984; Summerhayes et al. 1985). In general, New Zealand is considered to have a "clean environment" but this is not entirely the situation (McLay 1976; Ridgway & Glasby 1984). A reconnaissance survey of the geochemistry of lake and near-shore sediments in New Zealand showed evidence of high Pb and Zn contents in Wellington Harbour sediments for example (Stoffers et al. 1983). In this study, we present data on the distribution of selected heavy metals in Wellington Harbour sediments in an attempt to evaluate the importance of such pollution there. Because the amount of anthropogenically-derived metals depends largely on the input of wastes into the harbour, we commence with a statement on the history of waste input. A summary of the literature on pollution in the harbour is given by Davis (1982), Ridgway & Glasby (1984), and Wilson (1984) and this will not be duplicated here. A review of lead and cadmium in the marine environment is given by GESAMP (1984) and of lead in New Zealand by Anon. (1986).

HISTORY OF DOMESTIC AND INDUSTRIAL DISCHARGES Man's greatest impact on Wellington Harbour has occurred from the turn of the century. The growth and development of industry during this period led to a significant increase in the number of industrial, as well as domestic, discharges into Wellington waters. These were largely unchecked until the 1970s, when various factors, including the introduction and enforcement of water and soil legislation, a downturn in some industries, and increasing public awareness of pollution of the environment, led to a decrease in the number of polluting discharges.

New Zealand Journal of Marine and Freshwater Research, 1986, Vol. 20

496

LOWER HUTT

PETONE

Point Howard POINT HOWARD SEPTIC TANK ^ York Bay


Somes Island

i£:\

Mahina Bay

EASTBOURNE

Point Halswell Point Jerningham L.smbton Harbour

Mahanga Bay

Karaka Bay

Robinson Bay Point Arthur Camp Bay

WELLINGTON

Hinds Point

ARTHURS NOSE SEWER OUTFALU

M 0 7 p0|NT SEWER OUTFALL

Pencarrow Head

Island Bay Owhiro Bay THE SIREN ROCKS SEWER OUTFALL

Sinclair Head

ELSDON POINT SEWER OUTFALL

PENCARROW SEWER OUTFALL Fitzroy Bay

Fig. 1 Schematic diagram showing major sewer outfalls and reference points in Wellington Harbour.

Staffers et al.—Heavy metal pollution in Wellington Harbour

497

Table 1 Schedule of sewer outfalls in Wellington City (as at 27 March 1969).


Locality of discharge

Commencement Size of discharge (")

Johnsonville* Ngauranga*

1914 1909

18 24

Onslow Road* Kaiwharawhara* (North Outfall) Kaiwharawhara* (South Outfall) Shelly Bay* Moa Point Lyall Bay (Arthurs Nose) Hough ton Bay Island Bay South Karori

1938 1913

Type of treatment

Receiving water Ngauranga Stream Harbour

8 15

Septic tank Untreated (activated sludge since 1960s) Septic tank Septic tank

1908

6

Septic tank

Harbour

1899 1940

40 6

Septic tank Untreated Septic tank

Harbour South coast South coast

12 Untreated Twin 18 Septic tank 18 Untreated

South coast South coast South coast

1930 1909 1927

Harbour Harbour

*In July 1983, the last of these discharges was diverted to the main Moa Point sewage system.

Pre-1900 Before 1900, the most significant impact on water quality in local waters was from the discharge of domestic waste via sewers, stormwater drains, and open water courses. In 1890, with a population of 30 000. the volume of sewage discharged in Wellington was estimated at 7 megalitres per day (Mid 1 ) dry weather flow (DWF) (Beca CarterCaldwell Connell 1980). The main Moa Point outfall on Wellington's southern coast was commissioned in 1899 and is still in use with a present estimated DWF of 50 Ml d '. In addition, a number of smaller outfalls were constructed around the Wellington coastline to serve the growing population (Table 1).

Stream (in addition to meatworks and abattoir waste) and the discharge of tip leachate into the Horokiwi Stream from Cottles industrial tip, now no longer in operation. The Kaiwharawhara Stream received septic tank effluent, tip leachate, and industrial wastes including paints, zinc, and electroplating wastes. There were also minor discharges of domestic sewage at Shelly Bay and domestic sewage and industrial waste (mainly paint pigments) at Miramar which have been subsequently transferred to the Moa Point system. In July 1983, the Ngauranga and Kaiwharawhara discharges to the harbour were transferred to the main outfall at Moa Point by means of a newly constructed interceptor sewer and pumping station.

Domestic and industrial discharges In the Hutt Valley at the turn of the century, there was a number of industrial discharges directly into the Waiwhetu Stream and Hutt Estuary plus septic tank discharges from Upper Hutt into the Hutt River and from Lower Hutt into the Hutt Estuary and from Petone and Eastbourne directly into the harbour. Commissioning of the main outfall sewer in 1962 by the Hutt Valley Drainage Board (HVDB) enabled all domestic waste previously discharged into the Hutt River and the harbour to be pumped from Seaview to an outfall at Pencarrow located on the eastern approaches to Wellington Harbour (Fig. 1). In Wellington, several domestic and industrial discharges occurred adjacent to western harbour stream mouths. These were domestic sewage and industrial waste discharges into the Ngauranga

Meatworks discharges The most significant source of organic wastewater in terms of flow has for many years been from the two meatworks operating at Petone and Ngauranga and the Wellington City Council (WCC) abattoir also at Ngauranga. Since the establishment of the Gear Meat Company (Petone) in 1865 and the Wellington Meat Export Company (Ngauranga) in 1885, the effect of their effluents on harbour water quality has been dramatic. Data obtained for the Gear Meat Company indicate that at peak flow c. 10 kl d ' of effluent is discharged into the harbour at Petone (Table 2). Waste characteristics of the effluent also showed a wide range of pH and high levels of suspended and total solids, grease, and sulphides (Table 3). At peak, the combined discharge was estimated as being equivalent to the organic loading of a population of 300 000-400 000


498

Table 2 Geat Meat Company flow rates. Mean monthly flow (Ml d~') February 1972 December• 1979 June-Dec 1980

8.03 9.94 5.14


persons. The closure of the Ngauranga works in July 1973 and the transfer of the Gear wastes to the sewage system between December 1970 and November 1973 and its eventual closure in July 1981 resulted in a major improvement in the quality of harbour waters. Waiwhetu Stream and Hutt Estuary in the Wellington region

The major industrial area became established at Gracefield and Petone, particularly during the 1920s and 1930s. Factors favouring its location there included the availability of flat land, an underground water supply, rail transport, and the proximity to rivers and streams into which wastes could be discharged (Steven et al,. 1981). Over many years, industrial waste discharges were uncontrolled and consequently the Waiwhetu Stream and to a lesser extent the lower reaches of the Hutt Estuary were heavily polluted. In particular, metals were deposited in the Waiwhetu Stream in a variety of forms depending on the type of industry from which they had originated. Industries involved included electroplating that discharged zinc, chromium, and nickel in solution and sanding of metal products and welding activities which led to the deposition of zinc, iron, and nickel as metal fragments and fine particles. Zinc, lead, chromium, titanium, and iron were discharged as oxides and paint pigments. Lead was also discharged from battei-y processing. The addition of coloured dyes from dyehouse processing increased the visual impact of waste discharges. Other discharges contributed calcium carbide residues containing Ca(OH),, soaps and detergents, and large volumes of cooling water and boiler blowdown (Wellington Regional Water Board 1976).

The result of the discharges of various acids, sulphates, various alkalis, formalin, soaps, fats, oils, greases, paint residues, and heavy metals was to encumber the Waiwhetu Stream with high levels of BOD and COD, wide ranges of pH and temperature, and a variety of colours for many years (Wellington Regional Water Board 1976). Discharges of pollutants to the Waiwhetu Stream and the Hutt Estuary have now ceased as a direct results of the classification of the Hutt Catchment in 1968. Classification required all past discharges to be controlled by the regulations then in force. Temporary permits were granted, first by the Pollution Advisory Council and then by the Wellington Regional Water Board, that enabled industries to discharge waste legally until 1978 (Wellington Regional Water Board 1976). Completion of a trade waste sewer at that time meant that all trade wastes generated in the Gracefield area could be transferred to the HVDB Main Outfall Sewer. Enforcement of the HVDB's Trade Waste Bylaws has been the major influence in the upgrading of many discharges to the sewerage system. The control of anomalously high concentrations of toxic compounds and wide variations in pH and temperature has ultimately minimised the impact upon receiving waters at Pencarrow. In 1981, the total trade waste sewer flow from Gracefield averaged 4.5 Ml d ' (Steven et al. 1981). Inclusion of the Gracefield trade wastes to the main sewer in 1978 has been the last significant addition to the Hutt Valley sewerage system. The present situation

In contrast to the earlier years of the century, all industrial discharges into the harbour have been eliminated, either by closures to various industries or by diversions of discharges to the sewerage system. Only one major septic tank discharge remains at Point Howard and proposals are for it to be connected to the Pencarrow pipeline within a few years. Probably the major factors influencing harbour water quality at the present time are indirect discharges such as runoff from city streets and sewage

Table 3 Gear Meat Company effluent quality (from Hutt Valley Drainage Board records).

pH Suspended solids (ppm) Total solids (ppm) Grease (ppm) Sulphide (ppm)

October 1972 (4 samples) Mean Range

1974 (9 samples) Mean Range

11 1500

9.1-12.0 1200-1560

8.5 1880

4300

3965-5838

1000 35

386-1987 32-39

750 11

6.4-11.6 123-4870

60-2330 1.1-24.0

April 1972 12.45 p.m. 1.30 p.m. 10.8 1182

9.1 2284

1579

5822

163 103

_ 31

499


Stoffers et al.—Heavy metal pollution in Wellington Harbour from overloaded or leaking sewers which discharge via the extensive number of stormwater outlets. Periodic discharges from any of the 88 emergency sewer overflows can also have a significant localised effect on harbour water quality, particularly in Lambton Harbour and Evans Bay where tidal circulation patterns are restricted. Outside of the harbour, Wellington City and surrounding suburbs are still served by three major sewage outfalls (Table 4). Moa Point now serves greater Wellington (50 km2), South Karori serves Karori, and Island Bay serves a catchment of 17 km2 . Two minor discharges at Arthurs Nose and Houghton Bay still exist. Future Wellington City Council intentions are to eliminate firstly Island Bay and Houghton Bay and eventually Arthurs Nose discharges by their transfer to the Moa Point system. The Karori outfall, because of its remote location, is expected to remain separate from the one large service area discharging at Moa Point. Table 4 Average dry weather flows of major sewer outfalls (1984 data). -. figures not available. Authority

Location

wcc wcc wcc wcc wcc HVDB

Moa Point South Karori Island Bay Houghton Bay Arthurs Nose Pencarrow

Average D W F ( M l d ' ) 45.0 2.6 4.3 0.2 48.0

The composition of Wellington sewage

Mean concentrations of important constituents derived from regular monitoring between 1972 and 1984 indicate the Moa Point discharge is predominantly domestic but with a minor industrial component present (Table 5). In comparison, Hutt Valley sewage has a slightly higher industrial component in terms of metals, because of the greater number of metal-using industries in that area (Table 6). Overall, analyses of wastewater indicate that sewage generated in the Wellington region contains low levels of cadmium, chromium, nickel, and copper and normal levels of iron and zinc but high levels of manganese (natural) and lead (industrial) compared to overseas sewages.

SAMPLING AND ANALYSIS One hundred and seven surficial sediment samples and 20 cores up to 0.5 m long were collected at various locations in Wellington Harbour and adjacent areas (Fig. 2). The surficial sediments were

Table 5 Average composition of Moa Point sewage (Davis 1982). BOD5 = biochemical oxygen demand (5 day), COD = chemical oxygen demand, SS = suspended solids. Constituent BOD, COD SS NH, As Cd Cr Cu CN Fe Pb Hg Phenol Zn

Mean concentration (ppm) 200 370 200 16 0.01 < 0.002 0.31 0.36 0.11 0.67 0.06 < 0.0001 0.06 0.63

sampled mainly by diving. Seventeen samples were also taken from the Waiwhetu Stream (Fig. 3). Since heavy metals occur mainly in the clay-silt fraction of the sediment, the < 20 urn grain size fraction of the sediment was separated by sieving and the Atterberg method was used for chemical analysis. This method reduces the effects of grain size variations in the sediments. The samples were dried at 60°C and digested with HC1/HN0, (1:1). The trace metals Fe, Mn, Cu, Zn, Cd, Pb, Cr, and Ni were analysed with a Perkin Elmer model 403 atomic absorption spectrophotometer. A Scintrex HGG-3 flameless AA was used for the determination of Hg — 0.1 g of the samples was heated in quartz-glass tube up to 800-900°C and the total Hg content was analysed in a continuous airstream (1.5 1 mirr 1 ). Table 6 Average composition of Pencarrow sewage (Davis 1982). BOD5 = biochemical oxygen demand (5 day), COD = chemical oxygen demand, SS = suspended solids. Constituent BOD5 COD SS Fe Mn Zn Cu Ni Pb Co Cr

Mean concentration (ppm) 400 600 240 2.83 0.13 1.30 0.30 0.05 0.44 0.01 0.18

500


WELLINGTON


HARBOUR

Fig. 1 Schematic map showing sample locations in Wellington Harbour.

Stoffers et al.—Heavy metal pollution in Wellington Harbour

501

Chloride Batteries NZ Ltd.

Fig. 3 Schematic map showing sample locations in the Waiwhetu Stream.


The index of geoaccumulation is, therefore, a measure which compares present day heavy metal concentration with pre-civilisation background values. The background values used here are taken from lower sections of Wellington Harbour sediment cores (Table 7). The 'average shale' values are also included for comparison. Seven Igeo-classes were established based on the numerical value of the index:

To compare present day heavy metal concentration with pre-civilisation background values, we have used the index of geoaccumulation (Igeo) as introduced by Milller (1979). This index is defined as: Cn Igeo = log. 1.5 Bn where Cn is the measured concentration of the element n in the < 20 nm fraction of a sediment and Bn represents the geochemical background concentration of element n — either measured directly in pre-civilisation sediments of the area or taken from literature ('average shale' value). The factor 1.5 is introduced to include possible variations of the background values which are attributable to lithologic variations in the sediment.

Igeo

Igeo-class

>5 4-5

6 5

3-4 2-3

4 3

1-2 0-1

2 1

0

0

Designation of sediment quality Extremely contaminated Strongly/extremely contaminated Strongly contaminated Moderately/strongly contaminated Moderately contaminated Uncontaminated/moderately contaminated Uncontaminated

Each step, from one class to the next higher class, means a doubling of concentrations. Igeo-class 6, for example, means a concentration greater than 96 times above the background level. X-ray diffraction analyses were also carried out on a selected number of samples. SEDIMENT DESCRIPTION Textural analyses of the samples collected are in accordance with previous results by van der Linden (1966, 1967a). The inner harbour sediments are fairly uniform light olive grey (5Y 5/2) clayey silts with a sand content of generally less than 10%. The marginal sediments, including the Hutt River delta as well as the samples from the sewage outfalls at Moa Point and Pencarrow Head, are generally olive grey (5Y 3/2) to greyish black (N2)


502


4mm Fig. 4 Microphotograph of metal and coal particles from Station 102, Waiwhetu Stream.

depending on grain size and contain a large portion of sand. The high gravel content in some harbour sediments is mainly because of large shell fragments. Olive grey to greyish black sediments are also present at the wharf areas in Lambton Harbour. The greyish black colour clearly indicates anaerobic sediments. Sediments from the Waiwhetu Stream are moderate olive brown (5Y 4/4) to black (Nl) mainly anaerobic coarse sands to silty sands with very little clay. The harbour sediments are composed of quartz, feldspar, illite, and chlorite as the dominant mineral phases reflecting the abundant greywackes in the surrounding area. Pyrite and gypsum were found in a few Waiwhetu Stream samples. Anthropogenic particles identified in the samples include coal, glass, plastic, rubber, paper, cigarette filters, and metal fragments. The latter are especially abundant in the coarse fraction of some Waiwhetu Stream sediments (Fig. 4). As shown by energy dispersive analyses (ORTEC), these metal fragments vary greatly in their chemical composition. Particles rich in Fe are the most common; however, there are also fragments composed mainly of Ti and some contain high amounts of Pb, Ni, Cu. or Zn. Sulphur was detected in some samples. This is related to the presence of gypsum in the pores of the metal fragments.

CHEMICAL COMPOSITION A summary of the chemical composition of Wellington Harbour sediments is given in Table 8 and the data for Waiwhetu Stream sediments are given in Table 9. Compositional trends for selected elements for Wellington Harbour and the Waiwhetu Stream are mapped according to the index of gcoaccumulation (Miiller 1979) (Fig. 5, 6). For Wellington Harbour, Fe, Mn, Cr, and Ni are relatively uniform in composition in surface sediments and are in the general range of the background values for Wellington Harbour (cf. Table 7). Mn, Cr, and Ni, however, show some slightly higher values in the vicinity of the Hutt River delta. Cd is generally below the detection limit but higher values are observed in the vicinity of Lambton Harbour basin and Pencarrow outfall. Zn and Cu display low concentrations in the central basin of the harbour which are in the uncontaminated category and somewhat higher values off Petone. Moderate to strong levels of contamination of these elements are noted in Lambton Harbour basin and off Pencarrow and Moa Point outfalls (Fig. 5a, b). For Pb, the central basin of the harbour is moderately contaminated and somewhat higher concentrations are found in Evans Bay and off Petone and in the Hutt River (Fig. 5c). The Pb values off Petone tend to decrease with distance from the shore.

Staffers et al.—Heavy metal pollution in Wellington Harbour

503


WELLINGTON HARBOUR

- 6

Fig. 5A Schematic map showing distribution of zinc in Wellington Harbour.


504

WELLINGTON HARBOUR

>


•

•

= '

*

*

o

.

o o

• • •

^/-

8

y-

/

r^

^ I-

Cu •

Igeo-Classes /(

o

• • • • •

-

1 2 3 4 5

•

- 6

Fig. 5B Schematic map showing distribution of copper in Wellington Harbour.

Stoffers et al.—Heavy metal pollution in Wellington Harbour

505


WELLINGTON HARBOUR

Pb =

Igeo-Classes o • • • • •

-

0 1 2 3 4 5

• - 6

Fig. 5C Schematic map showing distribution of lead in Wellington Harbour.


508

Table 7 Heavy metal contents of the average of < 20 nm fraction of sediments from the lower sections of 5 Wellington Harbour cores and the 'average shale' value reported by Turekian and Wedepohl (1961). Cd values are in each instance taken from Turekian and Wedepohl (1961). Values are in ppm ur.less otherwise stated. Fe (%) Mn


Wellington Harbour cores Average shale

PD

Zn Cu Cr Ni Cd

Hg

3.20 347 20 86 13 80 21 0.3 0.165 4.72 850 20 95 45 90 68 0.3 0.4

Strongly contaminated values of Pb (Igeo class 45) are found in Lambton Harbour basin, off Pencarrow and Moa Point outfalls, and off Kaiwharawhara. A limited number of samples showing high Zn and Pb values were also analaysed for Hg (Table 9). These have a maximum value of 1.2 ppm. In the core samples studied.. Zn, Cu, and Pb show enrichment in the surface layers of the sediments, whereas the other elements show no such trend. This indicates that this is not a diagenetic enrichment but caused by pollution. Waiwhetu Stream shows moderate levels of pollution for Fe, Cr, and Ni, moderate to strong levels of pollution for Cu, Cd, and Hg, and extreme levels of pollution for Zn and Pb (Fig. 6a, b). Virtually

all Pb analyses belong to the extremely contaminated category. The highest Pb values recorded are in the Chloride Batteries drain (3.3%) and these decrease with distance from the drain. In the core samples, there is a pronounced variation in element concentrations with depth but it is not systematic. For two samples (one from the Chloride Batteries drain and the other from the Waiwhetu Stream), chemical analyses were obtained for the various sediment size classes (Table 10). These show a systematic decrease in concentration with increasing grain size for most of the elements studied. This indicates that the bulk of the metal pollution is held in the finest grain size of the sediments, probably by adsorption. In the Chloride Batteries drain, however, Pb is particularly enriched in the 20-125 urn size fraction (the maximum Pb value recorded is 24% in the 20-63 urn size fraction). X-ray diffraction and SEM studies showed that the Pb is held here as tabular and pseudohexagonal crystals of cerussite (PbCO3) and the enrichment of Pb in this size fraction is probably controlled by the size of the cerussite crystals. PbCO, is a stable form of Pb at pH values above about 5 (Stumm & Morgan 1970). The mobility of Pb in the sediments was studied by leaching experiments on two samples from Wellington Harbour and the Waiwhetu Stream using

Table 8 Summary of compositional data for sediments collected from various parts of Wellington Harbour. Fig. 2 shows the division of the harbour into the various areas considered here. Units are ppm unless otherwise stated, n, number of samples analysed. Fe (%) Mn

Cu Pb

Ni Cr

Area

n

A (Moa Poin;)

5 Mean 2.18 278 143 71 210 16 68 Max. 3.01 373 175 127 483 21 89 Min. 1.04 147 111 43 73 10 39 8 Mean 2.27 379 413 45 517 29 97 Max. 5.19 551 2270 216 6740 82 315 Min. 1.52 179 105 15 47 13 49 28 Mean 3.44 330 249 68 183 21 91 Max. 3.70 436 440 113 447 29 106 Min. 3.28 286 180 36 95 18 82 25 Mean 3.30 328 170 30 125 26 85 Max. 4.41 386 295 70 903 118 118 Min. 1.36 255 105 15 26 14 48 54 Mean 3.30 373 148 24 77 22 86 Max. 4.03 835 243 36 364 100 148 Min. 1.88 300 55 20 41 13 55 4 Mean 3.32 330 160 28 85 48 91 Max. 3.35 350 175 32 114 118 110 Min. 3.29 319 145 24 68 24 81 79 Mean 3.24 350 133 20 66 19 80 Max. 3.49 367 165 22 232 22 88 Min. 3.11 333 120 19 44 17 75

B (Pencarrow Outfall) C (Lambton Harbour basin) D (Kaiwharawhara and Ngauranga) E (Petone foreshore) F (Evans Bay) G (Wellington Harbour basin)

Zn

Stoffers et al.—Heavy metal pollution in Wellington Harbour the methods described by Forstner et al. (in press) (Table 11). The data show that most of the Pb in Wellington Harbour sediments is held in the moderately reducible phase of the sediments, whereas most of the Pb in the Waiwhetu Stream sediments is held in the easily extractable phase. This indicates that Pb in the Waiwhetu Stream sediments is highly mobile and that in the Wellington Harbour sediments much less mobile.

509

DISCUSSION The analyses presented above reveal that, on the whole, the central basin of Wellington Harbour suffers from only minimal heavy metal pollution. Local enrichment of Zn and Cu is observed in surface sediments from Lambton Harbour basin and off Pencarrow and Moa Point outfalls and this represents moderate to strong levels of pollution. A

Table 9 Heavy metal analyses ofWaiwhetu Stream sediments. The % < 20 (im size fraction on which the analyses were carried out is also given. Units are ppm unless otherwise stated.


Sample no. Sample location

Core depth (cm)

< 20 urn Fe (%) (%)

Zn

Cu

Pb

Cd

Hg Ni Mn Cr (ppb)

Right bank under pipe bridge Right bank under pipe bridge

0-5

47

4.20

370 178

2605

2.1 20 217 141

5-10

72

4.65 8690 173

6230

4.6 83 702 341 4810

99

Right bank under pipe bridge

17.5-22.5

44

4.40 6765 202

6340

5.1 72 753 355 5256

100

Left bank near large stormwater drain from Chloride Batteries

0-5

7

8.95 3905 448 25 695

3.9 73 121 241 4860

101


15-20

4

12.45 3575 879 24 790

4.8 54 400 371 2400

102


22.5-27.5

15

8.11 6600 560 25 490

7.5 83 463 609

103

Mid-stream 1 m from sample 4

5-10

6

8.06 3410 429 22 525

5.7 61 339 381 4920

104

Chloride Batteries drain

0-5

13

3.04

105

Chloride Batteries drain

0-5

14

4.25 1325 341 33 225

1.7 50 220 175

371

106

Right bank opposite large stormwater drain from Chloride Batteries

0-5

8

5.21 1110 194

2.9 29 254 144

378

107

Right bank opposite large stormwater drain from Chloride Batteries

10-15

35

3.37

108

Left bank under pipe bridge

0-5

48

4.44 5495 208 19 465

109

Left bank under pipe bridge

10-15

72

3.50

215

26

168