Replacing lead in an industrial fishing weight is not a single-material decision, it is an exercise in trading off properties that rarely point in the same direction. Lead has dominated the sector for decades precisely because it combined very high density, low cost and ease of casting in a way that is hard to match with a single substitute. Any real alternative has to solve that same balance: density, corrosion resistance in salt water, raw material cost and viability for industrial-scale manufacturing.
Why lead is so hard to replace in industrial fishing
With a density of 11.34 g/cm³, lead concentrates a lot of weight into a small volume, which allows for compact geometries without penalising the gear's hydrodynamic behaviour. It also melts at a low temperature (327°C), which greatly simplifies die-casting processes and reduces manufacturing energy costs. No alternative material matches this exact combination of density, melting point and cost; each one sacrifices at least one of the three variables.
However, these technical advantages do not offset lead's serious drawbacks. It is a highly toxic metal, both for human health and for marine ecosystems: it accumulates in sediment and the food chain, and prolonged exposure or ingestion is linked to documented neurological damage and other adverse effects. Every year, tonnes of lead are left on the seabed through gear loss or wear, contributing to silent, persistent pollution, since the metal does not degrade. This toxicity is precisely what has driven increasingly restrictive regulatory frameworks in Europe and growing pressure across the sector towards lead-free alternatives. Lead's ease of manufacture does not offset its long-term environmental and health cost, which is exactly the problem materials such as recycled zinc are designed to solve.
Five materials, five different trade-offs
Zinc alloys have a density of 6.6 to 7.1 g/cm³, noticeably lower than lead, but they melt at a low temperature and offer high resistance to marine corrosion. Of the five materials, it is the one best suited to high-volume die-casting, with a low raw material cost.
Tungsten solves the density problem, but not the scale problem. At 19.25 g/cm³, it is the only material that exceeds lead's density, which would allow equally compact geometries, and its corrosion resistance is very high. However, its extreme melting point (3,422°C) rules out conventional die-casting: in practice, tungsten weights are manufactured through powder metallurgy or resin composites, which introduces variability into the finished product and a very high cost that only makes sense for small weights in low production volumes, not for ballasting an entire industrial fleet.
Bismuth, with a density of 9.78 g/cm³ and high corrosion resistance, is the technically closest alternative to lead in terms of casting behaviour, as it also melts at a low temperature. Its high cost and mechanical brittleness, combined with a less established industrial-scale supply market, make it a less predictable option for continuous production orders.
Stainless steel solves the toxicity problem, but not the geometry problem. With a density of 7.7 to 8.0 g/cm³ and high corrosion resistance, it is durable and chemically inert in seawater, but its unsuitability for die-casting (it is machined or stamped, at medium-to-high cost) means weights have to be manufactured through processes that push up cost and limit the shapes achievable compared with a cast material. For gear that requires specific geometries, such as ballasting a bottom longline or balancing the float-to-weight ratio on a purse seine, this limitation is decisive.
Cast iron is cheap and dense (7.0 to 7.3 g/cm³, suitable for die-casting), but it shifts the problem onto corrosion: its resistance is low without constant surface treatment, and without it, it degrades rapidly in salt water, which over the course of a campaign in distant-water fishing grounds such as the Grand Banks, Newfoundland, Iceland or Norway compromises both its structural integrity and its working life.
Why zinc alloy for fishing weights is GreenCastSea's choice
Of all the materials assessed, recycled zinc alloy is the one that resolves the full balance without critically sacrificing any of the four variables: it maintains sufficient density for industrial ballasting, resists corrosion in seawater, is suited to large-scale die-casting processes, the technology GreenCastSea specialises in, and its cost allows both standard catalogue items and custom parts to be manufactured without the material becoming the limiting factor in an order.
This is the technical foundation behind our three ranges, all made from 100% recycled, lead-free zinc alloy, designed to deliver the operational performance industrial fishing demands without inheriting the environmental exposure of traditional lead.
Need fishing weights adapted to your gear or fishing ground? At GreenCastSea we also offer custom fabrication. Get in touch with our team and we will help you define the right solution.