Organochlorine and trace metal contaminants in the food web of the light-footed clapper rail, Upper Newport Bay, California

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Upper Newport Bay (UNB) is an ecological reserve of the California Department of Fish and Game and serves as refuge, foraging areas, and breeding grounds for a number of federal- or state-listed threatened and endangered species, including the Light-footed Clapper Rail or clapper rail (Rallus longirostris levipes). In 1996, the Santa Ana Regional Water Quality Control Board (SARWQCB) placed UNB and portions of San Diego Creek on the federal 303(d) list of impaired water bodies due to heavy and trace metal contamination (copper, cadmium, lead, selenium and zinc), pesticides (chlorpyrifos, dieldrin, chlordane, DDT) and PCBs. The many species of birds that nest or feed in Upper Newport Bay are an important receptor for these contaminants. One of the key steps in estimating the risk of contaminant exposure to birds is to determine the contaminant concentrations in various components of their diet and surrounding environment as well as direct measures of exposure (ie. bird eggs). This study is providing data to support the development of the Toxics TMDLs in the San Diego Creek watershed by determining the concentration of selenium (Se), heavy metals, and organochlorine compounds in the food web of the clapper rail. The objective of this study is to: 1) determine the concentration and degree of bioaccumulation of heavy and trace metals (including selenium), and organochlorine compounds in three components of the Upper Newport Bay ecosystem: nonviable clapper rail eggs, benthic macrofauna, and sediments and 2) evaluate contaminant impacts on clapper rails by examining nonviable eggs for evidence of egg shell-thinning or embryo developmental abnormalities that have been linked to these contaminants.

This study found that DDTs (including 2,4'-DDT, 4,4'-DDT and its metabolic products 2,4'- DDD, 2,4'-DDE, 4,4'-DDD, and 4,4'-DDE), technical chlordane compounds, selenium, and mercury are present and biomagnifying in the food web of the Light-footed Clapper Rail in Upper Newport Bay. Of these compounds, 4,4’-DDE is the contaminant of greatest concern. The rationale for this finding lies in 1) DDE concentrations exceed screening levels for sediments and bird eggs and 2) embryonic abnormalities and eggshell thinning occur in a clapper rail egg that contains elevated DDE concentrations. Selenium concentrations in clapper rail eggs were below levels considered to impair reproduction. Because of the limited number of egg samples analyzed, it is recommended that additional data be collected to test the hypothesis that DDT, Se, and Hg may be causing ecologically-significant effects to rail reproduction. Although rates of biomagnification of DDTs in clapper rails relative to prey organisms (126-874 fold) were high, DDT concentrations in prey organisms (0.75 – 32 ng g-1 wet weight (wt)) were well below levels that have been shown to be acutely toxic to clapper rails feeding on them (LC50 of 3.2- 3.8 x105 ng g-1 wet wt). This suggests that DDT contamination is not causing avian mortality in Upper Newport Bay. However, chronic impacts, such as reproductive impairment, genetic mutations, etc. can occur at levels several orders of magnitude below acute toxicity thresholds. DDT concentrations in some Upper Newport Bay samples exceed a risk-based dietary screening level for clapper rails (17 ng g-1 wet weight) computed from the EPA NOAEL for pelicans. However, DDT concentrations measured in the clapper rail prey organisms are below lowest observed adverse effect levels (LOAELs) for significant reproductive impairment in studies reviewed by EPA, including the LOAEL for pelicans, which appear to be the most sensitive of avian species (150 ng g-1 wet weight).

Screening values for chronic reproductive impairment from total DDT are not currently available for the clapper rail, so comparisons were made using screening values from other omnivorous aquatic birds when available. The maximum DDE concentration found in the egg from Nest Site 5 (1050 ng g-1 wet wt) is below that which caused reduced clutch size, decreased productivity and increased incidence of shell cracking in the white faced ibis (3000 ng g-1 wet wt); but 4,4’- DDE was found in all 6 clapper eggs at concentrations exceeding levels of the lower range of the level of concern for biotic effects in omnivore waterfowl (250 ng g-1 wet wt). This suggests that DDT could be causing some degree of reproductive impairment of clapper rails in Upper Newport Bay. Observation of minor eggshell thinning and developmental abnormalities in the rail egg with the highest DDE concentration further supports cause for concern that DDTs may be causing some degree of reproductive impairment of clapper rails in Upper Newport Bay.

Indications are that impairment due to DDTs is likely declining; DDT concentrations in clapper rail eggs measured in this study are less than previously measured in UNB during the 1980s. In addition, UNB is currently home to the greatest number of clapper rail breeding pairs in southern California, a number that has nearly doubled from 103 in 1982 to 174 in 2004. Notably, clapper rails feed at a lower trophic level than shorebirds. Consequently, the results of this study should be considered in conjunction with results of other studies that provide data for higher trophic level feeders when developing TMDLs for the San Diego Creek watershed.

The lack of PCBs and chlordane in sediments, prey organisms, and the low levels in rail eggs indicates that these contaminants are not likely to be of concern in the food web of the UNB clapper rail population. Average concentration of total PCBs found in UNB clapper rail eggs (94 ng g-1 wet wt) was an order of magnitude below levels thought to be of concern for decreased hatching success in chickens – the bird species most sensitive to PCBs found to date. Levels of total PCBs found in UNB clapper rail eggs (94 ng g-1 wet wt) were an order of magnitude below levels thought to be of concern for decreased hatching success for Aroclor 1242 in chickens – the most sensitive bird species to PCBs found to date (870 ng g-1 wet wt). Levels of chlordane components and metabolites in rail eggs (30 ng g-1 wet wt) did not exceed “no effect” thresholds.

All other organochlorine compounds were at non-detectable concentrations in sediments, prey organisms and eggs1. The majority of sediment samples from the five nest sites had Se concentrations which exceeded levels considered to be of substantive risk to aquatic life (> 4 mg kg-1 dry wt); Se concentrations in prey organisms (3.6-9.8 mg kg-1 dry wt) in several cases exceeded projected dietary screening values indicating a substantive risk to fish and wildlife (> 7 mg kg-1 dry wt). Despite the fact that UNB rail egg Se concentrations were elevated relative to those in other southern Californian salt marshes, Se concentrations in UNB rail eggs were below threshold of marginal risk to aquatic birds (<6 mg kg-1 dry wt). In the egg that exhibited abnormal development from Nest Site 5, selenium toxicity did not appear to be the likely cause. The reason for this conclusion is due to the relatively low selenium concentration in the egg and lack of apparent deformities in the embryo that are characteristic of selenium, such as reduced or missing eye. While a combined effect of DDE, Se, and/or other contaminants may be responsible for the deformity, it is not possible to definitively determine the cause. 1Minimum detection limits for chlordane, toxaphene and dieldrin were below numeric TMDL targets established for sediments in the San Diego Creek watershed.

Of other trace elements, metals, and metalloids, Hg was the only contaminant whose concentrations were sufficiently elevated in UNB sediments, prey organisms and rail eggs to be of concern. Hg, as well as several other elements (Co, Cu, Pb, Ni, Ag and Zn), had sediment concentrations exceeding threshold effects levels (TEL) values. Only Hg, however, exceeded dietary screening levels in three of the primary prey organisms of the clapper rail (crabs, isopods, and snails; 0.15-0.2 mg Hg kg-1 dry wt). Mean Hg concentration in UNB clapper rail eggs (0.64 mg kg-1 dry wt) exceeded the no effect level, but only one egg (1.3 mg kg-1 dry wt) was within the lower range of the level of concern. Based on these results, it is highly unlikely that Hg is impairing clapper rail reproduction in UNB.

Due to the exclusive use of non-viable eggs, these results present a worst-case scenario appropriate for a screening level study. Because of this issue, along with the limited sample size and extent of spatial sampling in the estuary, we recommend further study to determine the extent to which DDTs, mercury and selenium may be currently impairing reproduction of the clapper rail in Upper Newport Bay. Such a study would complement ongoing studies examining organochlorine contamination in the food webs of UNB fish and fish-eating birds.

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