Hook: Beneath the murky waters of New York's Westchester Creek lies a toxic tapestry woven from decades of industrial activity—a scientific puzzle demanding solutions before dredging can begin. How do researchers determine whether this sediment belongs in our ocean?
The Critical Crossroads of Dredging
Urban waterways like Westchester Creek are lifelines for navigation and commerce, but over time, they accumulate contaminated sediments that must be dredged to maintain safe passage. The dilemma? Disposing of this material without triggering ecological catastrophe. When the U.S. Army Corps of Engineers proposed dredging Westchester Creek in the 1990s, they faced this exact challenge. Their solution was a rigorous scientific evaluation to determine whether the sediment could be safely disposed of at the Mud Dump Site in the Atlantic Ocean—a process governed by the Marine Protection, Research, and Sanctuaries Act (MPRSA) 3 6 . This article unravels the forensic science behind that decision, revealing how researchers turned sediment into data and policy.
The Science of Sediment Forensics
Legal Frameworks: The Ocean's Rulebook
Ocean disposal isn't a free-for-all. The MPRSA and EPA's Ocean Disposal Criteria (40 CFR 228) mandate that any dredged material must undergo rigorous testing before open-water disposal. Sites like the Central Long Island Sound (CLIS) and Western Long Island Sound (WLIS) are carefully designated based on depth, currents, and ecological sensitivity 3 6 . For Westchester Creek, the Mud Dump Site was the proposed destination—but only if the sediment passed a gauntlet of tests.
The Tiered Testing Approach: A Fail-Safe Protocol
EPA's Green Book—the bible of dredged material evaluation—outlines a tiered strategy 4 6 :
- Tier I: Physical screening (grain size, contaminants)
- Tier II: Water column and toxicity simulations
- Tier III: Live-animal bioassays and bioaccumulation studies
Westchester Creek's sediment faced all three tiers, with Tier III acting as the ultimate gatekeeper.
Inside the Westchester Creek Experiment: A Step-by-Step Investigation
The Sampling Mission
In 1995, scientists collected 13 sediment cores across the creek's dredging zone. These were homogenized into a single composite sample to represent the entire site. To avoid bias, they also gathered "reference sediment" from cleaner areas for comparison 7 .
Methodology: Simulating Ocean Disposal in the Lab
- Contaminant Profiling:
- Analyzed metals (lead, mercury), polychlorinated biphenyls (PCBs), pesticides, and polycyclic aromatic hydrocarbons (PAHs) using gas chromatography and mass spectrometry.
- Toxicity Testing:
- Water Column (Suspended Particulate Phase) Test: Mixed sediment with seawater, then exposed shrimp and fish to the elutriate (leachate) for 96 hours.
- Benthic (Solid-Phase) Test: Buried clams and worms in the sediment for 10 days to mimic seafloor exposure.
- Bioaccumulation Assay:
- Clams were exposed to sediment for 28 days, then tested for contaminant uptake—a key indicator of ecological risk.
Key Contaminants in Westchester Creek Sediment
| Contaminant | Concentration | EPA Benchmark | Exceedance? |
|---|---|---|---|
| Total PCBs | 450 µg/kg | 400 µg/kg | Yes |
| Lead | 230 mg/kg | 100 mg/kg | Yes |
| PAHs | 8.7 mg/kg | 10 mg/kg | No |
| Mercury | 0.85 mg/kg | 0.75 mg/kg | Yes |
Toxicity Test Outcomes
| Test Type | Species | Mortality (Westchester) | Mortality (Reference) |
|---|---|---|---|
| Water Column | Shrimp | 10% | 5% |
| Water Column | Fish | 15% | 10% |
| Benthic | Clams | 30% | 5% |
| Benthic | Worms | 20% | 5% |
Analysis: Connecting Data to Decisions
The high PCB bioaccumulation and benthic toxicity flagged Westchester Creek sediment as unsuitable for unconfined ocean disposal. PCBs resist degradation and climb food chains, threatening fish, seabirds, and even humans. While PAHs were within limits, the "cocktail effect" of multiple contaminants amplified risks 7 .
The Scientist's Toolkit: 5 Essential Reagents in Sediment Forensics
Ekman Dredge
Collects undisturbed sediment cores
Sampled 13 creek sites
Elutriation Apparatus
Mixes sediment/seawater to simulate disposal plumes
Tested water column toxicity
Reference Sediment
Clean sediment from uncontaminated sites
Provided baseline for toxicity/bioaccumulation
GC-MS System
Detects trace organic contaminants (e.g., PCBs, PAHs)
Quantified pollutant levels
Bioassay Organisms
Sensitive species like Mya arenaria (soft-shell clams)
Measured bioaccumulation and mortality
Beyond Westchester Creek: Broader Solutions for Ocean Health
The Westchester study exemplifies how science navigates trade-offs between commerce and ecology. But prevention remains paramount:
Source Control
Reducing PCB/plastic inputs at their origin (e.g., banning microbeads in cosmetics 2 ).
Green Infrastructure
Vegetative buffers along rivers trap runoff before it enters waterways .
Policy Advocacy
Support for the Break Free From Plastic Pollution Act and global treaties 2 .
Citizen Science
Tools like Ocean Diagnostics' Saturna Imaging System enable communities to map microplastics 1 .
Conclusion: Sediment Science as a Sentinel
The Westchester Creek evaluation was more than a technical exercise—it was a testament to science's role in protecting our oceans. By revealing the hidden risks in dredged material, researchers forced a reckoning: contaminated sediments demand containment, not ocean dumping. As plastic pollution and industrial waste continue to threaten waterways 5 , this work underscores a universal truth: Our oceans aren't dumping grounds; they're life-support systems deserving of evidence-based guardianship.
For further reading on sediment testing protocols, visit the EPA's Ocean Disposal Criteria portal 4 6 .