Time for lesson two of boating school! Today, let’s steer our gaze to how heavy metals in antifouling paint impact soils in situ and further away from the site.

How do heavy metals end up in soils? 

After each sailing season when time comes for repainting the hull, the loose paint fragments containing heavy metals are shed by sanding, scraping and washing (Eklund & Eklund, 2014). This causes the paint particles to end up on the ground. When it rains, heavy metals from the paint get leached out in situ, contaminating the soil (Lagerström, Norling & Eklund, 2016). This problem is exacerbated with the absence of proper regulations and appropriate disposal methods. For instance, a national survey by the Swedish Transport Agency in 2010 revealed that 82% of boat owners do not have the access for the safe collection and disposal of paint particles shed (Lagerström, Norling & Eklund, 2016). 

Groundwater pollution may also occur when infiltrating rainwater leach the paint particles, delivering the pollutants to the groundwater. In another scenario, the pollutants may spread far away from the source. The heavy metals may also leach into runoff, transporting the toxic leachates to other environments. Runoff may also directly mobilise the paint particles on the ground, transporting them to far away aquatic environments and soil patches, where leaching then occurs there (Lagerström, Norling & Eklund, 2016). Hence, polluted soils present far-reaching consequences as they can redistribute and accumulate the heavy metal pollutants in aquatic environments (more about this in the next post!). 

Effect of heavy metal pollution on soils 

Heavy metal pollution has been proven to be harmful to the diversity and biological activities of microbial communities in soils (Wang et al., 2007; Jin et al., 2015). Soil microbes are extremely important in the detoxification of chemicals, maintenance of soil structure, recycling of plant nutrients, control of pests and plant growth (Wang et al., 2007). As such, elevated concentrations of heavy metals disrupt the stability of the soil microbes, resulting in subquality soils crucial for species richness, plant growth and the functioning of ecosystems (Wang et al., 2007). Furthermore, toxic heavy metals can make its way into the food chain through plants (Wang et al., 2007) since plants are on the lower trophic level. 

Case study: Boatyards in Sweden 

In order to illustrate the gravity of heavy metal pollution on soils, we’ll turn to a study done by Lagerström, Norling and Eklund (2016) on recreational boatyards near Lake Mälaren in Sweden. Alarmingly, for Boatyard A, it was found that 65% and 71% of the data points surveyed for Cu and Zn respectively exceeded the less sensitive land use (LSL) guideline of 200mg/kg and 500mg/kg (red rectangle on diagram)! 

It was also revealed that for the average boat club, 137g of Cu and 633g of Zn contaminate the soil every sailing season due to biofouling removal alone (excluding other activities such as scraping and sandpapering). This well exceeds the LSL guideline by 23 and 43 times for Cu and Zn respectively! 

Furthermore, based on the diagram above, just 4 years (between 5 and 9 years) of boat maintenance on unprotected soil is sufficient to substantial increases of Cu and Zn in soils (blue rectangle on diagram). This means that the longer an area is used for boat maintenance without proper disposal methods, the higher the concentrations of heavy metals. This is a pressing issue which should be formally regulated as soon as possible. 

The scary fact about heavy metals is that they are persistent. Over the past 25 years, the use of lead (Pb) in antifouling paints has decreased substantially, with red lead (Pb3O4) being phased out in 1995 (Lagerström, Norling & Eklund, 2016). However, if you look at the previous diagram, Pb is still present in topsoils where boats have been stored for longer periods (50 years). This is because Pb out-competes other metals for binding sites and binds to organic matter in the soil well (Lagerström, Norling & Eklund, 2016). 

That’s all on soils! In our final “lesson”, we’ll look at the fate of the poor animals suffering from our leisure activities.

 

References: 

Eklund, B. & Eklund, D. (2014) Pleasure boatyard soils are often highly contaminated. Environmental Management. 53(5), 930-946. Available from: 10.1007/s00267-014-0249-3. 

Jin, Z., Li, Z., Li, Q., Hu, Q., Yang, R., Tang, H., Li, M., Huang, B., Zhang, J. & Li, G. (2015) Canonical correspondence analysis of soil heavy metal pollution, microflora and enzyme activities in the Pb–Zn mine tailing dam collapse area of Sidi village, SW China. Environmental earth sciences. 73(1), 267-274. Available from: 10.1007/s12665-014-3421-4.

Lagerström, M., Norling, M. & Eklund, B. (2016) Metal contamination at recreational boatyards linked to the use of antifouling paints—investigation of soil and sediment with a field portable XRF. Environmental Science and Pollution Research. 23(10), 10146–10157. Available from: 10.1007/s11356-016-6241-0.

Wang, Y., Shi, J., Wang, H., Lin, Q., Chen, X. & Chen, Y. (2007) The influence of soil heavy metals pollution on soil microbial biomass, enzyme activity, and community composition near a copper smelter. Ecotoxicology and environmental safety. 67(1), 75-81. Available from: 10.1007/s11434-008-0355-9.

Images:

Dailymotion (2018) SpongeBob SquarePants – S06E16 – Boating Buddies. Available from: https://www.dailymotion.com/video/x6vhzcf [Accessed 30 August 2020].