Metallic mangroves: Sediments and in situ diffusive gradients in thin films (DGTs) reveal Avicennia marina (Forssk.) Vierh. lives with high contamination near a lead-zinc smelter in South Australia

From 1889, aerial emissions and effluent from a coastal lead-zinc smelter at Port Pirie, South Australia, have led to the accumulation of lead (Pb), zinc (Zn), arsenic (As), cadmium (Cd) and copper (Cu) in the surrounding marine environ-ment. Despite this, extensive stands of grey mangrove (Avicennia marina) inhabit coastal areas at Port Pirie, right up to the smelter's boundary. To understand the contamination level the mangroves are living in there, elemental concentra-tions were measured in mangrove sediments, leaves, pneumatophores and fruits at sites 0.30-43.0 km from the smelter. Plant health was assessed via leaf chlorophyll content at four sites with contrasting contamination, as well as in situ labile elemental concentration using diffusive gradients in thin films (DGT). Sites < 1.7 km of the smelter exceeded Australian and New Zealand Environment and Conservation Council (ANZECC) & Agriculture and Resource Management Council of Australia and New Zealand (ARMCANZ) (2000) sediment quality guideline values for As (78.3-191 mg/kg), Cd (5.17-151 mg/kg), Cu (80.7-788 mg/kg), Pb (2,544-14,488 mg/kg) and Zn (281-62,097 mg/kg), while sites further away showed less enrichment above background. Similarly, elevated elemental concentra-tions in leaves and pneumatophores occurred closer to the smelter (up to 319 mg/kg Pb; 1,033 mg/kg Zn), while fruits had little contamination of non-essential elements (<= 5.23 mg/kg). Relationship between sediment and leaf elemental concentration was isometric for Pb and anisometric for others. Labile As, Cd, Cu, Pb and Zn exceeded the 95% and 80% level of species protection in marine water by ANZECC & ARMCANZ (2000) near the smelter, but chlorophyll content did not vary significantly among sites (p > 0.05). These results reveal that A. marina tolerate high elemental contam-ination at Port Pirie, contributing to lesser but still high contamination in plants, warranting further investigation into non-lethal impacts on mangroves or additional biota inhabiting this ecosystem.

Automated summary

Since 1889, a lead-zinc smelter in Port Pirie, South Australia, has caused the accumulation of heavy metals in the marine environment. However, grey mangroves (Avicennia marina) are still able to tolerate high levels of contamination. The study found elevated concentrations of heavy metals in the mangrove sediments, leaves, pneumatophores, and fruits, indicating the need for further investigation into the impacts on the mangroves and other organisms.