Effluent impacts case study: The River Mersey Bird MortalityBird Mortality

The River Mersey is formed from the confluence of industrialised tributary rivers which arise in the Pennine hills above Manchester, in NW England. The river runs

Table 1.5 Pollution examples from the mining industry. ExamplePollutantActivityCausesCommentsExample References Wheal Jane, Cornwall, UK 1992Iron & other trace metals, low pHAbandoned tin mineRising groundwater after mine closureCarnon River & Fal Estuary discoloured; peak contamination of metals 900xEQS Zn

Younger et al. 2005 King River, TasmaniaCopper, sulphidic acidsCopper miningEffluentLocher, 1995; Dowson, 2003 Phalaborwa Mine, South AfricaLow pH, metals, aquatic toxicityCopper, zinc & phosphate miningDust, tailings dams overflowing, discharges

Rivers in the Kruger National Park (KNP), bioaccumulation in aquatic organisms, water not drinkable at camps in KNP Heath & Claassen, 1999; Kotze et al. 1999 Blesbokspruit South Africa (gold mining, & paper factory)

Sulphate (salts), iron and trace metals Abandoned mine & closure of pulp & paper factory Rising groundwater after mining ceased & no appropriate closure or responsibility for liability Acid mine drainage required treatment to protect a Ramsar wetland

Ambani & Annegarn, 2015 Ecuador 2000Mercury & cyanide, trace metals

Artisan gold miningPrimitive mining and processingExtensive impacts, small scaleTarras-Wahlberg et al. 2000 Mining impacts, UKIronMainly abandoned coal minesRising groundwater after mine closure400–600 km affected by ferruginous drainage, UKYounger, 2000

Industrial pollution and the water environment 9 from Manchester for 113 km to the sea in Liverpool Bay. The Mersey Estuary has an extensive inner basin, flanked on the south side by the Manchester Ship Canal, which received effluent from a lead anti-knock (tetra-alkyl lead) plant in Ellesmere Port (Figure 1.1). Following a steadily improving trend in water quality during the 1980s, fish began to return to the estuary (Wilson et al. 1986) and the estuary supported large numbers of over-wintering wildfowl and wading birds.

In September 1979, sick and dead wading birds, plus a handful of waterfowl, began to be noticed by bird watchers at a ringing station in Hale, on the north bank of the upper estuary, and by wildfowlers on the marshes along the south bank. Both local groups stated that the phenomenon was highly unusual and they suspected pollution.

Analysis of the dead birds revealed elevated concentrations of lead in liver and other tissues. But the concentrations were lower than in some estuaries draining lead-mining catchments (e.g., Gannel in Cornwall), where there were no bird mortalities.

Figure 1.1 Photo-diagram illustrating the scene of the 1979 Mersey Bird Mortality, NW England, UK (Photo credits: BJ D’Arcy).

In any such investigation, it is by no means always clear which are the chemicals to be investigated in an effluent brew of product, process side reactants, raw materials and the spectrum of forms in between. Associated Octel Company (AOC), the manufacturer of the lead anti-knock product, conducted their own investigations and analysis for their product and its tri-alkyl lead water soluble, stable, break-down derivatives. They informed the investigators in North West Water of their belief that the pollutant affecting the birds was tri-alkyl lead. The bird mortalities continued through October 1979, ceasing in November. The company co-operated fully with the investigations and no-one was initially able to explain why the incident should occur suddenly in 1979. Subsequent laboratory tests dosing starlings with alkyl lead replicated the symptoms observed in the dying birds, and post-mortem analysis of the starlings revealed comparable tissue concentrations of lead to those found in the dead/sick wading birds from the Mersey (Osborne et al. 1983). The organic form of lead was not only water soluble, but more fat soluble than inorganic lead. That greater availability seemed likely to explain why mortalities occurred at elevated total lead concentrations, but lower than might be expected from estuaries polluted by inorganic

lead from historic mining activity. Why did this occur in 1979? One theory was that the spat ‘bloom’ of the small estuarine shellfish Macoma balthica which was noted in the upper estuary, provided a preferred food species which bioaccumulated the lead, replacing the more usually available (in the Mersey) worms in the diet of the birds; the shellfish had five times the lead concentration of the worms (Maddock & Taylor, 1980;

Wilson et al. 1986). The last detail which needed to be resolved was the fact that the AOC discharge was into the tidal reach of the Manchester Ship Canal, (MSC), not the Mersey. The environmental compartments from process effluent to biota were:

Process effluent → MSC water → Estuary water → biota → birds

→ man (wildfowlers)

Earlier investigations had shown that the Ship Canal only passes relatively small flows out into the Estuary during the drier summer months (and neap tides), via lock gates at the mouth of the canal. But when the largest tides (spring and autumn) equal or exceed the design level in the canal, lock gates at the canal mouth and also upstream in Runcorn are opened and draw water – with the accumulated daily load of alkyl lead from AOC – upstream to spill into the upper estuary at Runcorn (D’Arcy & Wilson, 1978). That process is in addition to the normal tidal movements and dispersal of pollutants up and down the estuary on every tide. A review of the discharge permit for AOC was undertaken and new limits agreed, based on correlations between dead birds and effluent concentrations, plus a safety allowance for possible sub-lethal effects on birds. Birds were taken as the critical environmental factor (see Table 1.6); the evidence predicted an increasing risk of bird mortalities at a discharge in excess of 6 mg/l soluble lead. Similar levels would be likely to result in liver concentrations in excess of the 0.5 mg/kg threshold identified by Osborne et al. (1983). The limiting load was therefore agreed with the discharger, and target environmental quality standards for soluble lead were derived for estuary water.

Table 1.6 Correlation coefficients for alternative regressions (y = mx + c) for levels of alkyl lead in various environment compartments.

Y X R n

No. dead birds (all spp.) Concentration in Macoma balthica 0.90 14 Concentration in Mersey Estuary water Discharge load 0.87 48 No. dead birds (all spp.) Discharge concentration (mean

previous month)

0.81 17

No. dead birds (excluding gulls) Discharge concentration (mean previous month)

0.77 17

Concentration in MSC Discharge concentration 0.76 27

No. dead birds (all spp.) Discharge concentration (monthly mean)

0.71 17

Concentration in Macoma balthica Estuary water concentration 0.68 288

Concentration in Macoma balthica Discharge load 0.65 288

Source: Adapted from Wilson et al. (1986).

Industrial pollution and the water environment 11 When water quality standards were exceeded in subsequent years, as predicted dead and sick birds again began to be found. This case study illustrates the difficulties in protecting the water environment when regulating a large number of potentially toxic effluents discharged to a large complex water body and investigating and preventing pollution problems, even with the full co-operation of the industries there. It should be noted that alternative theories were put forward to explain the mortality (Smith et al. 1982), but were not given priority over the case for tightening controls at the AOC factory (by the company and the regulator).

Process controls improved discharge quality consistently by 1983 (D’Arcy et al.

1999). The plant is still operational, reprocessing tank farm sludge contaminated with alkyl lead, from petrochemical plants around the world (AW Wither, pers.

com. 2015).

1.3 INDUSTRIAL COMPLEXES – POINT SOURCE