By Jack Shaw, senior writer and editor at Modded
Historically, pressure-treated wood has been the default choice for docks, boardwalks and other waterfront structures. It resists rot, insects and constant moisture better than untreated lumber, helping property owners build longer-lasting infrastructure.
However, some of the chemicals used to preserve wood can gradually leach into surrounding waterways as the material weathers. While residential use of some treated wood preservatives changed some years ago, many older waterfront structures remain a contamination threat today.
Why Did Pressure-Treated Wood Become the Standard?
For much of the 20th century, waterfront construction faced the simple truth that wood and water don’t mix well. Constant moisture encourages rot, while insects and marine organisms can quickly weaken untreated timber. Replacing docks, piers and boardwalks every few years wasn’t practical or affordable, especially for large commercial properties and marinas.
Pressure-treated wood offered a solution. During the manufacturing process, preservatives were forced deep into the wood under pressure. This helped it resist decay and insect damage for far longer than untreated lumber. One of the most widely used chemical preservative systems was chromated copper arsenate (CCA), which combined copper to control fungi, arsenic to deter insects and marine pests and chromium to help bind those chemicals to the wood fibers.
From the 1970s until December 2003, CCA-treated timber became a common choice for residential decks, play structures, fences and many waterfront applications because of its durability and relatively low maintenance requirements. Although manufacturers voluntarily phased out most residential uses of CCA-treated wood due to health risks, pre-2003 structures that used it remain in service today.
How Does Chemical Contamination Spread?
According to the most recent completed U.S. Environmental Protection Agency’s National Rivers and Streams Assessment, 47% of U.S. rivers and streams are in poor condition for at least one biological health measure. This reflects the cumulative impact of various pollution sources and nationwide habitat degradation. Chemical contamination comes from many sources, including:
- Agricultural runoff: Fertilizers, pesticides and animal waste can wash into nearby waterways.
- Industrial activities: Manufacturing facilities and historical industrial sites may release metals and other contaminants if not properly managed.
- Urban stormwater: Rainwater can carry oil, heavy metals, road salt and other pollutants from streets and parking lots into rivers and lakes.
- Aging infrastructure: Older pipes, bridges, bulkheads and pressure-treated waterfront structures can contribute contaminants as materials deteriorate over time.
Unlike many pollutants that eventually break down, metals such as arsenic, chromium and copper don’t simply disappear once they enter the environment. Instead, they can accumulate in water and nearby sediments, where they remain available to aquatic organisms for extended periods.
Over time, contamination can affect both ecosystem health and the people who rely on these waterways for recreation and other uses. Once a chemical like arsenic enters water supplies, it can cause acute and long-term health effects, as it’s a carcinogen.
Legacy Contamination Matters
Pressure treatment significantly extends the life of wood, but it doesn’t permanently lock every preservative compound in place. Over time, exposure to rain, waves, sunlight and changing temperatures gradually weathers the surface.
Under certain environmental conditions, small amounts of preservative components can migrate from treated wood into the surrounding soil, sediment and water. Several factors influence how much preservative may leach from treated wood over time:
- Age of the structure: Older wood gradually weathers, exposing treated surfaces and increasing the likelihood of preservative components migrating.
- Water type: Freshwater and saltwater environments can influence how preservatives behave over time.
- Temperature: Warmer conditions may accelerate weathering and affect leaching rates.
- Sunlight or UV exposure: Prolonged UV exposure slowly breaks down the wood’s surface, contributing to natural deterioration.
- Wave action and abrasion: Constant movement, impacts and physical wear can increase surface erosion.
- Quality of the original treatment: The treatment process and the extent to which preservatives bond to the wood can influence long-term performance.
Why Do Consumers Rarely Hear About Chemical Leaching?
Most waterfront property owners unintentionally continue to contribute to environmental degradation, unaware of the impacts their docks and aquatic structures have. In many cases, the issue receives little attention because:
- Many older structures are still standing: Older docks and boardwalks continue to leach toxins.
- The change happened gradually: Manufacturers voluntarily phased out CCA-treated wood for most residential uses, quietly avoiding an immediate nationwide ban.
- The effects aren’t always visible: Unlike an oil spill or algae bloom, chemical leaching occurs slowly over time and often goes unnoticed.
- Property owners often inherit existing infrastructure: Many people purchase waterfront properties with docks already in place and may not know what materials were used.
- Durability has historically driven purchasing decisions: Builders and property owners have traditionally prioritized longevity and maintenance costs over the long-term environmental footprint of construction materials.
- Cost affects choices: Wood is traditionally seen as an affordable material, so many owners never investigate alternatives.
What Laws Regulate CCA Exposure in Water?
Certain industrial applications of CCA-treated timber continue, but the Environmental Protection Agency’s Clean Water Act helps to protect waterways by governing how hazardous substances are stored and managed by facilities near water. While the focus is on spill-prevention, property owners also have some responsibility, depending on local environmental regulations and the condition of their infrastructure.
However, these regulations primarily focus on preventing new sources of contamination rather than on replacing aging infrastructure installed decades ago. For many waterfront owners, decisions about repairs and replacements present the greatest opportunity to reduce future environmental impact.
Why Are Modern Waterfront Materials a Solution?
Modern waterfront construction offers more options than treated timber alone. Composite materials, aluminum and modular floating dock systems have become increasingly common because they reduce maintenance and require fewer preservatives than traditional wood treatment.
For example, high-density polyethylene (HDPE) is a polyethylene thermoplastic that naturally resists rot or insect damage. It is also UV-resistant and less temperature sensitive. HDPE modular dock systems can remain in service for decades with relatively little maintenance, such as painting, staining or applying protective coatings. Wood docks only have an average service life of a decade. They may be able to last longer with intensive chemical-based maintenance.
Full Life Cycle Mindset on Materials
Some alternatives, such as plastic-based materials, require a closer look. Without responsible manufacturing and end-of-life management to minimize waste and prevent material loss into the aquatic environment, these are sustainable in name only.
Manufactured materials that contain harmful substances are often used in the automotive and boating industries. The same material properties can transfer to related environments with high sun exposure. Plastics often contain toxic chemicals, such as lead, bromine and polyvinyl chloride (PVC), which may release volatile organic compounds into the atmosphere and water. PVC is a popular choice with auto and boating manufacturers, and may even be used in some synthetic dock products.
Durability remains an important consideration for any waterfront project. The most sustainable material may not have the lowest up front cost or the longest lifespan alone. It should also minimize maintenance demands, reduce environmental risks throughout its service life, and support responsible replacement or recycling when that lifespan ends.
Whether you’re upgrading a residential dock or planning commercial waterfront infrastructure, considering the full life cycle of construction materials helps balance performance with long-term environmental stewardship. Material choices made today can continue to affect surrounding waterways for decades.
Frequently Asked Questions About Chemical Leaching
Here are common questions and answers to help you better understand waterfront construction and its environmental considerations.
Is pressure-treated wood still used for waterfront construction?
While CCA is no longer produced for most residential applications, certain pressure-treated wood products remain available for commercial, industrial and specialized uses. New docks may use this treated timber, which can continue to poison waterways by leaching different preservative chemicals.
Are all modern dock materials environmentally friendly?
Every material has a trade-off. Pressure-treated wood can release preservative components over time, while plastic-based materials may require responsible manufacturing to avoid releasing VOCs during warmer weather. Polyethylene thermoplastics, such as HDPE, offer the best use case, with minimal waste and material loss. Evaluating a product’s full life cycle provides a more complete picture of its environmental impact.
Should an older treated wood dock be replaced immediately?
While ideal for preventing the release of toxins, when a dock should be removed depends on its condition, safety and maintenance requirements, as well as local regulations. When replacement becomes necessary, it’s worth comparing modern materials that can reduce ongoing maintenance and eliminate the need for chemical wood preservatives.
Look Beyond Tradition to Preserve the Waterfront
CCA pressure-treated wood resolved engineering challenges and made waterfront construction more practical for several generations. However, as scientists’ knowledge of the environment expands, the long-term effects of some preservation systems have become apparent. The impact of exposure to harmful chemicals on human health underscores the urgency of moving toward more sustainable systems in water-based construction.
Many waterfront infrastructure projects can remain in service for decades, which is why they are unlikely to be removed from marinas or riverbanks. These structures continue to leach harmful chemicals, including arsenic, into the water system. Safer, longer-lasting options are available, and responsible waterfront property owners should choose them.
Author Bio
Jack Shaw, the senior writer and editor at Modded, specializes in weaving together the threads of health and wellness with greater concerns about sustainability best practices and industry developments. With a commitment to providing actionable insights and empowering readers, Through his writing, Jack seeks to educate and inspire individuals on their journey toward more eco-friendly decisions. Feel free to connect with him via LinkedIn.