Potential risk of lead sinkers in the freshwater environment

Lead sinkers enter the aquatic environment when they disconnect unintentionally or intentionally from fishing gear. As fishing is big in The Netherlands and lots of anglers frequent the same locations, densities of lead sinkers in the sediment can be high. Such concentration of lead could have potential detrimental effects on aquatic biota, such as invertebrates, fish or other wildlife.

However, it should be noted that lead has different speciation in the aquatic environment and that it is especially the dissolved Pb2+ that is cause for concern. Invertebrates are exposed to dissolved lead, while larger animals can also ingest sinkers while foraging for food. The ‘stichting Gezond Water’ has asked the Science Shop of Wageningen University & Research whether it is possible to investigate the potential environmental risks of lead sinkers for the freshwater environment.

According to the researchers, available data from various measurement locations show that the annual average throughout the Netherlands is below the environmental quality requirement (JG-MKE) of 1.2 µg/L of free dissolved lead, only sporadically is a measured value above 1.2 µg /L reported. In addition, the toxicity of lead appears to depend on water conditions, such as suspended matter in the water column, water hardness, and pH.

A dose-effect relationship has been investigated with water snails, with 4 different densities of 3 mm split lead (0, 4, 20, 100 leads per pot with 1 liter of water) both with and without a layer of 2 cm fine sediment. The water snail Physella acuta did not experience any effects of lead on mortality, but compared to the control group, the growth of the snails was significantly lower at 4 lead per pot with 1 liter of water with sediment.

The researchers' conclusion is that it is still difficult to estimate the realistic risk to aquatic animals of dissolved lead released from fish lead in Dutch water systems. This requires more insight into, for example, the lead density at popular fishing locations, the extent to which the fish lead lies on the sediment surface, the dilution factor (flow rate), the sedimentation speed of suspended particles (lead cover), and the influence of dredging.