The Proposed Auckland Unitary Plan


In Scope 39 we discussed the upcoming issue of the Proposed Auckland Unitary Plan (PAUP) 2013 containing provisions not allowing the use of unpainted metal roof (or wall) cladding. This includes ZINCALUME ® which has a surface 80% of aluminium, and ignored the large number of galvanised roofs dating back up to 100 years. The NZMRM/NZ Steel position has been that in the 20+ years that Zincalume ® has been the predominant roof cladding, the zinc run-off levels (certainly those from metal roofs) have been steadily decreasing as galvanised/zinc roofing has been steadily replaced with ZINCALUME®.

We also had this discussion with the previous ARC in 2005/6. At that time Dr.Bryan Shedden of Bluescope Australia made a presentation to the Auckland District Councils based on work done by NZ Steel and NZMRM which showed that the level of zinc run-off from Zincalume® was minimal.

At the time this was accepted as clearly showing that from roofing alone by far the greatest level of zinc run-off came from galvanised (100% zinc coating) roofs of various ages. These of course constituted at the time (pre-ZINCALUME®) the majority of Auckland (and NZ) roof cladding.  A report by the then Auckland City Council at about the same time showed that a significant and steadily increasing contribution to zinc in stormwater in fact came from motor vehicle tyres which contain zinc oxide, and which of course increases steadily as does the traffic.  
In September 2014 in a technical paper to the Water New Zealand Conference in Hamilton, Dr.Shedden delivered a thorough critique in great and technical detail on the theory that zinc run-off from metal roofing is actually harming aquatic biota, and demonstrated that it is not.

This is far too long and complicated to publish here in its entirety although as a published document it is available, on the Water NZ website -

In September Dr.Shedden and various expert witnesses presented at the PAUP hearings on Topics 046 and 049, and we now have to wait until next year for the outcome.  However, it is important to grasp the basics of what could significantly increase roofing costs across New Zealand if accepted.

Here Dr Troy Coyle of New Zealand Steel summarises the key findings from this important presentation, as well as other relevant publications.


Auckland Council’s Position on Source Control for Roofing

Zinc in stormwater has been identified by Auckland Council as a priority contaminant of concern for Auckland harbours, estuaries and streams, evident in the source control measures specified in the Proposed Auckland Unitary Plan (PAUP). The PAUP restricts the installation of “high contaminant-yielding roofing, spouting, cladding material or architectural features” product to not exceed:

1) 25m2 in urban environments, or rural environments where run off is piped directly to a watercourse; and

2) 250m2 in rural environments where run-off is directed to vegetated drain/swale, wetland or similar. For roofing and cladding areas larger than the 25m2 (urban, roughly the size of a carport) or 250m2 (rural, roughly the size of a house), this becomes a controlled activity and the stormwater must be discharged through devices that will limit the concentration of total zinc to <30.0µg/l.

Auckland Council does not identify any environmental effects justifying the 30.0µg/l zinc target. The figure is derived from a median value performance of a range of best management practice zinc reduction approaches (Auckland Council, 2013)1 and has not been linked to any data relating to environmental effects. Council bases its concerns on observations of temporal trends in contaminant concentrations for marine sediment, with Council claiming that some sites have shown increasing zinc levels.

What does the data tell us about zinc trends in Auckland waterways?

A more recent study identifies serious concerns with the reliability of Council’s zinc trend claims (Shedden, 2014)2 . In his study, Shedden reviewed Council’s own monitoring data (derived from a range of sources including National Institute of Water and Atmospheric Research Ltd and Diffuse Sources Ltd) and concluded that “where statistically significant trends occur for zinc levels in streams, estuaries and harbours, they are mostly observed to be reducing”. He found that zinc levels in the vast majority of marine sediment sites have not changed significantly during the monitoring period. In addition, his analysis of temporal trends for zinc in freshwater streams revealed that no sites are experiencing increasing levels of zinc. Shedden confirmed that freshwater streams, in particular, were consistently observed to have declining levels of zinc over the last two decades of monitoring, with almost half the monitoring stations showing significant decreasing trends between 1995 and 2013.

Shedden’s findings are consistent with comprehensive stormwater contaminant modelling of the Upper Waitemata Harbour and South-eastern Manukau Harbour, which predicted a decreasing trend in zinc loads between 2001 and 2015-20 as existing galvanised roofs are replaced by zinc aluminium coated steel, followed by a slow increase as vehicles become the dominant source of zinc (Timperley and Reed, 2008 )3.

The New Zealand roof and wall cladding market has been almost completely converted from heavy usage of galvanised steel following the introduction of zinc aluminium coated steel to New Zealand in 1994. As such, Shedden et al, 20074  predicted that the net zinc load from steel roofing in the urban Auckland region would be reduced by 95% for modern steel roofing (unpainted and prepainted zinc aluminium coated steel) compared with past usage of galvanised steel. From a national perspective, the Parliamentary Commissioner for the Environment (2012)5  has stated that heavy metal pollution is largely a legacy issue arising from old industry practices, and from a scientific perspective, the three key water quality contaminant issues for New Zealand are actually pathogens, sediments and nutrients. Consequently, instituting zinc source control for roofing is not justified as it would have no significant impact on environmental health.

What other data exists to support Auckland Council’s position?

To determine the impact that zinc might have on an environment, we would need to know four key things:

1. the baseline levels of zinc that are naturally present in that environment;

2. the zinc levels that the environment can tolerate without any more than minor adverse effects;

3. any trends in zinc concentration levels, which, as discussed above, Shedden (2014) has shown to be predominantly decreasing in Auckland waterways; and

4. the bioavailability of the zinc present in that system, which the literature suggests reduces when the zinc binds with organic matter in soil/sediment and reduces as stormwater travels downstream.

Baseline Levels of Zinc

Data relating to baseline zinc levels in the Auckland region are not extensive. This is important data to have because some systems have what might at first seem relatively high naturally occurring zinc levels, e.g. due to the chemistries associated with local geological features. For example, measurements on an uncontaminated river (the “Kleine Nete” in Belgium) show that a high quality ecosystem has an average total zinc concentration of 60.0 μg/l, with concentrations ranging from <20.0 μg/l to 140.0 μg/l (Van Assche, van Tilborg and Waeterschoot, 19966 ). It is worth noting that these ranges are consistent with total zinc concentrations measured in Auckland waterways and reported in Shedden (2014). It is also worth noting that soils in the Auckland region are often volcanic in nature, and are therefore naturally rich in metals that would be considered contaminants in other environments.

Zinc levels that the Auckland Environment could tolerate without any more than minor adverse effects

Zinc at environmental levels (i.e. indirect exposure via the environment) does not create human health problems (Bodar, Pronk and Sijm, 20057). In fact, the World Health Organisation considers zinc deficiency to be a widespread human health issue with around thirty-one percent of the global population having a deficiency in zinc, contributing to almost one million deaths per annum (Caulfield and Black, 20048 ).

Since zinc is an essential element for life, any given ecological community will have an optimal range of zinc concentrations. This limit has not been defined for Auckland waterways. The amount of metal added to natural waters that is required to produce a given biological response, such as a reduction of growth, is different for different waters (Allen, 19969). While no studies have been identified that specifically review optimal zinc concentrations for Auckland waterways, it has been reported that optimal zinc concentrations range between 1.0-50.0 µg/l for European alluvial lowland river habitat (Van Assche, van Tilborg and Waeterschoot, 1996) and that a zinc benchmark (though it is not defined if this is an upper threshold) of 120.0 µg/l is considered protective to marine and freshwater life (State of Oregon Department of Environmental Quality, 2014)10.

Van Sprang et al. (2009) predicted a “no effect concentration” for zinc to be between 22.1 µg/l and 46.1 µg/l in European river basins. Median total zinc in fresh water streams in Auckland ranges from 1.0 µg/l to 44.0 µg/l, with only one site at 110.0 µg/l (Shedden, 2014). Thus, the reported zinc concentrations in Auckland waterways and the predominant trend towards declining levels of zinc in those waterways (Shedden, 2014), combined with the lack of reported cases of zinc toxicity and Auckland zinc concentrations being predominantly within the optimal zinc levels reported in the literature, suggest that there is not a high risk of any more than minor adverse effects from zinc in surface water.

Auckland Council has undertaken benthic health analyses to investigate benthic health in coastal sediments, specifically focusing on concentrations of total lead, copper and zinc  (Anderson, Hewitt, Ford, and Thrush, 2006; Hewitt and Ellis, 2010; Lohrer, Hewitt and Townsend, 2012). What has not been shown is that measures designed specifically to reduce zinc (and only zinc) runoff into stormwater will improve benthic health. The individual effect of zinc in the system, differentiated from the effects of other contaminants and sedimentation has not been determined. This is important as contaminant levels will tend to be higher when sedimentation rates are elevated. When compared against international sediment quality guidelines (such as ANZECC, 2000), it appears that the vast majority of sediments tested in the Auckland region have only low levels of zinc contamination, “thereby offering a high level of protection for sediment-dwelling species” (Shedden, 2014).

Bioavailability of Zinc in Auckland Waterways

Bioavailability refers to the rate and extent to which a particular form of zinc might be taken up by an organism (Wallinder et al., 2001). When determining environmental effect, the bioavailability of the zinc needs to be considered (Van Assche, van Tilborg and Waeterschoot, 1996). This is because not all forms of zinc are bioavailable. Most zinc in runoff is likely to be present as hydrated Zn2+ ions, which is the most bioavailable zinc form (Heijerick, et al., 2002; Wallinder, et al., 2001). However, in marine sediment, zinc is no longer likely to be in a bioavailable form due to the availability of complexing organic and inorganic compounds.

There was no evidence in the literature reviewed to demonstrate that zinc in sediment is readily available to benthic organisms. Since several papers report that soil will remove the majority of zinc in runoff, including the bio-available form (Bertling et al., 2002), it does seem reasonable to assume that zinc in sediment is not bioavailable to benthic organisms. Therefore, any conclusions regarding environmental effects that have been based on marine sediment zinc studies are unlikely to be reliable.

Zinc concentration in runoff and its bioavailability will decrease by “several orders of magnitude” after it is released to surface water (Heijerick, et al., 2002). The presence of organic matter and suspended solids can also lead to a major decrease of metal bioavailability (Heijerick, et al., 2002). Therefore, any risk of environmental effect is rapidly attenuated by removal, dilution and reduction in bioavailability as stormwater travels downstream (Brix et al., 2010). Further, Brix et al. (2010) warned that “collection of stormwater samples directly from rooftops results in samples that are in considerable disequilibrium with the environment” and this contributes to “overestimation of impacts from stormwater runoff when the default assumptions used to assess point source discharges are applied”.


Where statistically significant trends in zinc levels in Auckland waterways occur, they are mostly observed to be declining, particularly in freshwater systems. The market’s move away from galvanised steel roofing to bare zinc aluminium coated steel roofing, which has only 10-15% of the zinc runoff levels of galvanised steel, is likely to significantly reduce zinc runoff from roofing. There have been no reported cases of zinc toxicity in Auckland waterways and zinc concentrations reported for Auckland waterways appear to be consistent with zinc concentrations reported elsewhere in the literature, and trending downwards. Therefore, given the evidence base for declining zinc levels, the lack of demonstrable environmental effects and the consistency with optimal zinc levels reported in the literature, Auckland Council’s stringent regulatory approach to zinc source control via control of bare zinc aluminium coated steel roofing and cladding is unjustified.

1 Auckland Council. (2013). Auckland Unitary Plan Stormwater Management Provisions: Technical Basis of Contaminant and Volume Management Requirements. Auckland Council Technical Report 2013/035.

2 Shedden, B. (2014). Critical Review of Zinc Trends in Auckland Streams, Estuaries and Harbours. Water NZ Conference, (p. 17). Hamilton.

3 Timperley, M., and Reed, J. (2008). Central Waitemata Harbour Contaminant Study. Development of the Contaminant Load Model. Prepared by NIWA Ltd for Auckland Regional Council. Auckland Regional Council Technical Report 2008/038.

4 Shedden, B., Batchelor, J., and Chizmar, J. (2007). Roof Runoff Study by New Zealand Metal Roofing Manufacturers.

5 Parliamentary Commissioner for the Environment (2012) Water Quality in New Zealand: Understanding the Science. Parliament New Zealand, 93 pp.

6 Van Assche, F., van Tilborg, W., and Waeterschoot, H. (1996). Environmental Risk Assessment for Essential Elements Case Study: Zinc. International Workshop on Risk Assessment of Metals and their Inorganic Compounds (pp. 171- 180). International Council on Metals and the Environment.

7 Bodar, C. W., Pronk, M. E., and Sijm, D. T. (2005). The European Union Risk Assessment of Zinc and Zinc Compounds: The Process and the Facts. Integrated Environmental Assessment and Management, 301-319.

8 Caulfield, L. E., and Black, R. E. (2004). Zinc Deficiency. In Comparative Quantification of Health Risks: Global and Regional Burden of Diseases Attributable to Selected Major Risks (pp. 257-279). World Health Organisation.

9 Allen, H. (1996). Importance of Speciation of Metals in Natural Waters and Soils to Risk Assessment. Report of the International Workshop on Risk Assessment of Metals and their Inorganic Compounds, (pp. 141-157).

10 State of Oregon Department of Environmental Quality. (2014). Reducing Zinc in Industrial Stormwater Fact Sheet. State of Oregon Department of Environmental Quality.