USGS







TOXICITY OF FRESH VERSUS

EQUILIBRATED PORE WATER

By

Parley V. Winger and Peter J. Lasier
Patuxent Wildlife Research Center
University of Georgia
Warnell School of Forest Resources
Athens, Georgia 30602

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ABSTRACT
INTRODUCTION
OBJECTIVE
METHODS AND MATERIALS
RESULTS AND DISCUSSION
SUMMARY AND CONCLUSIONS

Abstract

Pore water is considered a primary route of contaminant exposure to benthic organisms. Used with solid-phase sediment evaluations, toxicity of pore water provides additional insight into the bioavailability of contaminants to benthic organisms. However, toxicity and chemistry of pore water change in response to sediment disturbance, and the complex chemistry commands careful interpretation of results. The objective of this study was to evaluate the influence of a one-week equilibration period (sediment storage) on pore-water toxicity. To accomplish this, toxicity of pore water collected immediately after stirring the sediment was compared with that of pore water collected after one week of equilibration (sediment stored in the dark at 4oC). Toxicity was determined using percent survival of Hyalella azteca exposed (static) for 96 hours to pore water collected from the sediment with vacuum extractors. Toxicities of contaminated sediments were generally more pronounced in pore waters collected after one week of equilibration compared to those extracted immediately after stirring. Alkalinity, hardness, conductivity and ammonia increased and pH decreased following sediment storage. Although increases in toxicity of some pore waters were attributed to the elevated ammonia concentrations, toxicities of some pore waters were due to other factors such as contaminants. Pore-water assessment is a useful tool in the determination of sediment quality, but standard operating procedures that include specific guidance on sediment disturbance and storage time (equilibration period) after disturbance should be followed to reduce variability and enhance interpretation of test results.

Introduction

Pore water is a primary route of contaminant exposure to benthic organisms. Used with solid-phase testing, pore water provides additional insight into sediment bioavailability of contaminants. However, toxicity and chemistry of pore water change in response to sediment disturbance and storage time, and the complex chemistry of pore water commands careful interpretation of test results. Disturbance (stirring) of the sediment during solid-phase testing increases the turbidity and amount of material in the pore water, thus influencing the availability of contaminants in the pore water. Storage or holding of disturbed sediment should allow an equilibrium between the sediment and pore water to re-establish itself. This study was undertaken in order to evaluate the influence of sediment storage time/equilibration on pore-water chemistry and toxicity.

Objective

Determine the influence of sediment equilibration (sediment storage after disturbance) on the toxicity and chemistry of pore water.

Methods and Materials

yellowba.gif (924 bytes) 85 sediments collected
    - Canals in Dade County Florida
yellowba.gif (924 bytes) Sediments re-homogenized
yellowba.gif (924 bytes) Pore water extracted
    - 500 mL with vacuum extractors
    - Aerated for 15 min.
    - Basic chemistry measured
yellowba.gif (924 bytes) Five replicates of each sample
    - 30 mL glass beaker
    - 20 mL pore water
    - 1 cm square Nitex netting
    - 10 Hyalella azteca
yellowba.gif (924 bytes) 96-h exposure
    - 23 C
    - 16 h light:8 h dark
yellowba.gif (924 bytes) Survival as the endpoint
yellowba.gif (924 bytes) Pore water extracted 8 d after sediment disturbance
     - Sediment equilibrated in dark
     - Stored at 4 C
yellowba.gif (924 bytes) Pore water testing repeated



Figure 1: Flow Chart of Methods


Figure 2: Photo of Equipment Setup



Comparison of toxicity in fresh pore water versus equilibrated (sediments stored 8 d) pore water from sediments collected from Dade County, Florida.

No Significant Difference Signif. Higher Toxicity Significantly
Less Toxic
Toxic 1 Toxic 1 Notox1 Notox1 Toxic 1 Notox1
Toxic 2 Notox2 Notox2 Toxic 2 Toxic 2 Toxic 2
C1000101 C1020101 AC0101 C1020204 C12N0104 C100B0101 C1W0102
C1030101 C10A0101 AC0102 C1030301 C13N0101 C10101 REF5
C1030201 C40201 AC0103 C20201 L31E0102 C1020301
C1110101 C60301 BD0101 C40301 MI0102 C50102
C1110201 C10C0101 GL0101 MI0103 C60101
C1N0101 C1W0201 L290201 WC0104 GL0102
C20301 C20101 L290101
C50101 C30101 L31E0202
C60201 C40102 L31N0101
L31E0301 C40103 MI0101
C40202 REF6
C40302 REF8
C60102
C60202
C60302
C60401
C60402
FC0101
L300201
L31N0201
PP0101
REF (3)
CONTR. (7)
RECON (7)
ORF(7)

Results and Discussion

Equilibration (storage) of sediments tended to increase the toxicity of pore water. Pore waters that were toxic initially generally became more toxic, and several (14% of this data set) that were not toxic in the initial tests became toxic after sediment storage for eight days. Of the 23% (20 samples) that decreased in toxicity, only 8% (2 samples) were significantly less toxic. Only 14% (12) of the samples showed no difference in survival (toxicity). Some increases in toxicity were attributed to increases in ammonia and alkalinity that occurred during storage; however, some metals increased in the pore water also. Hardness and conductivity also increased in the pore water with storage, but pH decreased.

Summary and Conclusions

yellowba.gif (924 bytes) Toxicity of fresh vs equilibrated pore water
     - Equilibration - storage 8 d
     - 85 comparisons
     - 96-h exposures of Hyalella azteca
yellowba.gif (924 bytes) Over 60% increased in toxicity with storage
     - 34% were significantly toxic
     - 14% became toxic
yellowba.gif (924 bytes) Most basic chemical parameters increased
     - Ammonia, conductivity, alkalinity, hardness
     - DOC and some metals increased (Cr, K, Ni, Mg)
     - Some metals decreased (Al, As, Cd, Cu, Pb)
     - pH decreased
yellowba.gif (924 bytes) Equilibration after sediment disturbance important
     - Pore-water toxicity
     - Pore-water chemistry

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