Mining waste report identifies research gaps. PHOTO |COURTESY
By PATRICK MAYOYO
Areas requiring more information
- Understanding behaviour of sediment plumes; physical and chemical behaviour of pollutants through the marine ecosystem.
- Modelling of plumes (horizontal shearing and upwelling) and the resulting tailings footprint.
- Enhanced toxicity testing to assess impacts to deep-sea ecosystems.
- Understanding the ecological significance of smothering all benthic organisms in the disposal site footprint and physically altering the bottom habitat.
- Identification of the reduction in species composition/abundance and biodiversity of marine communities.
- Determining and understanding the significance of bioaccumulation of metals through food webs and ultimately into human fish-consuming communities; and potential increases in risk to human health.
- Assessing recolonization potential of deep-sea benthos and limiting factors by deep-sea benthos; timescale for recovery of impacted areas.
- Specialized sampling equipment for the deep-sea.
More scientific research needs to be done to understand and assess the environmental impacts of wastes from mining operations which have been disposed into the marine environment, a new report shows.
The Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) report, Impacts of mine tailings in the marine environment, provides the findings of an international workshop held in Lima, Peru (in 2015) and makes a number of recommendations for future work.
The report notes that there are major gaps that need to be addressed in the scientific understanding of the behaviour of mine tailings in the sea at depths greater than 20m to 80 m and consequently the short- and long-term impacts on the marine environment and other potential users of marine resources.
Scientific gaps in measurement and monitoring techniques in assessing impacts of existing and proposed new deep-sea discharges of mine tailings need to be addressed.
Since the workshop, GESAMP has established a dedicated working group to assess the environmental impacts of wastes from mining operations which have been disposed into the marine environment, under the co-lead of IMO and UN Environment.
A number of large-scale mines worldwide use marine or riverine disposal for mine tailings, under Government permits.
The GESAMP International Workshop of the Impacts of Mine Tailings in the Marine Environment was held in Lima, Peru, in June 2015 and attended by 90 participants.
The workshop was hosted by the Marine Authority of Peru (DICAPI) and organised as a joint IMO-DESAMP activity.
Findings and conclusions
Overall, the workshop concluded that there are major gaps that need to be addressed in the scientific understanding of the behaviour of mine tailings in the sea at depths greater than 20 to 80 m and consequently the short and long term impacts on the marine environment and other potential users of marine resources.
Furthermore, scientific gaps in measurement and monitoring techniques in assessing impacts of existing and proposed new deep-sea discharges of mine tailings need to be addressed. Although much is known about impact assessment methods in the upper ocean, further work is needed regarding how to conduct impact assessments in the upper stratified ocean waters.
However, much more needs to be done to extend and modify physical, chemical, and biological assessment techniques developed for surface waters in order to apply them to the deep sea.
Gaps in scientific information and measurement techniques
Gaps in the current science and information/understanding of deep-sea ecosystems as well as the behaviour of mine tailings in the marine environment were emphasized.
These abiotic and biotic processes and techniques include physical oceanography (e.g. plume behaviour and modelling), chemistry, and impacts to ecological systems in the deep sea, such as impacts to the composition and functioning of the pelagic and benthic communities.
- Marine organisms normally used for toxicity testing are from the upper stratified layers of marine water, not the deep sea. There is a need to develop standard sediment and aquatic toxicity tests that use species from deeper water. While the preference would be to conduct in situ testing with marine species in the deep sea, that is recognized as both complicated and costly. Toxicity test issues that should be addressed include:
- The use of suitable test temperatures;
- Incorporating pressure into laboratory experiments where possible to simulate the deep-sea environment;
- The measurement of bioavailability and bioaccumulation in the deep sea;
- Chronic studies with variable exposure regimes/scenarios;
- The use of a wide taxonomic range of marine species; and
- Expanding available toxicity tests to represent tropical marine environments.
- There is a need to better understand the physical and chemical behaviour of mine tailing slurries and sediment plumes in the deep sea, including empirical work and modelling. Available current studies are generally from surface currents, not the deep sea. Issues include:
- Spatial and temporal variability of horizontal and vertical gradients of currents, and physical and chemical properties of the water-column; and
- Shearing off and fate of plumes and suspended sediments after discharge into the water column, in view of such factors as currents, flocculation, characteristics of the tailings, and deep-sea pressures. The dynamics of deep-sea canyons and sporadic events such as benthic storms or dense shelf water cascading also need to be addressed.
- The toxicological effects (and their significance) of mine tailings in the water column, at the disposal site, and in the far field need to be better understood. Key elements:
- Deep-sea exposure pathways need to be understood;
- The significance of physical smothering of benthos, and the impact of bioavailable fractions of heavy metals upon biota;
- Understanding of the effects on abundance and biodiversity, and the relationship (i.e. impacts) to biota in the upper stratified waters;
- Sensitivity of fauna to suspended loading, and recovery dynamics; and
- Cumulative effects over long periods of time (e.g. 50 years), possibly from multiple sources.