Article pubs.acs.org/est
Polybrominated Diphenyl Ethers (PBDEs) Alter Larval Settlement of Marine Intertidal Organisms across Three Phyla via Reducing Bacterial Abundance on the Biofilms Jill M. Y. Chiu,† Beverly H. K. Po,‡ Christine Y. S. Chan,‡ Michael H. W. Lam,§ Pei-Yuan Qian,∥ and Rudolf S. S. Wu‡ †
Department of Biology, Hong Kong Baptist University, Kowloon, Hong Kong SAR, China School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China § Department of Biology and Chemistry, City University of Hong Kong, Kowloon, Hong Kong SAR, China ∥ Division of Life Sciences, Hong Kong University of Science and Technology, Kowloon, Hong Kong SAR, China ‡
ABSTRACT: Polybrominated diphenyl ethers (PBDEs) have been widely used as flame retardants over the last three decades, and are now ubiquitous in the marine environment. While the harmful effects of PBDEs on the abnormal development and reproductive impairment in mammals and fish are well documented, the effects on marine invertebrates remain virtually unknown. Using three model intertidal species accross three phyla, including the polychaete Hydroides elegans (Phylum Annelida), the gastropod Crepidula onyx (Phylum Mollusca), and the barnacle Balanus amphitrite (Phylum Arthopoda), this study demonstrated that (a) chronic exposure to BDE-47 (at spiking concentrations up to 1000 ng L−1) throughout the entire larval stage did not affect settlement, development or growth of all three species per se, despite bioaccumulation was clearly evident (measured body burden ranging from approximately 7000 to 13 000 ng BDE-47 g−1 lipid), and (b) BDE-47, at measured concentrations of 15 and 113 ng g−1 lipid, reduced the bacterial abundance in biofilms and resulted in a concomitant change in larval settlement pattern of all the model intertidal species across three phyla.
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of 70.7 and 28.1 pg L−1 have been reported in the dissolved phase and suspended particulate matters in Hong Kong seawater, respectively.19 Recent studies have reported that the concentrations of PBDEs in marine mammals and Ardeid eggs from South China could be up to 51 100 and 1000 ng g−1 lipid, respectively.14,20,21 High levels of PBDEs have also been reported in fish (up to 246 ng g−1 lipid) and various marine invertebrates (e.g., up to 1055 ng kg−1 wet wt in oysters) in the South China region.22,23 These studies provide clear evidence that PBDEs contamination is very serious in South China and Hong Kong. The vast majority of our existing knowledge on the biological effects of PBDEs is based on studies of mammals, and to a lesser extent, fish. In mammals, acute toxicity of PBDEs is low, but chronic exposure may be teratogenic and lead to impairment of neuro-development, liver enlargement and hyalin degeneration in kidney.4,10 Previous studies in rats have also indicated that PBDEs are endocrine-disruptors, and
INTRODUCTION Polybrominated diphenyl ethers (PBDEs) have been widely used as flame retardants in plastics, textiles, resins, building materials and electronic equipment since the 1970s.1,2 Commercial PBDEs primarily consist of mixtures of tetra-, penta-, octa-, and deca-BDEs.3 The harmful effects of pentaand octa-BDEs on humans have been well documented,4 and correspondingly their production has been banned by the European Union and United States in 2004.2,5 In contrast, there is no regulation over the production or usage of PBDEs of all kinds in Asia thus far, including China. PBDEs levels in the environment, wildlife, and humans saw an alarming increase in the last 30 years;4,6−8 for instance, their levels in human blood, milk and tissues have doubled every five years.9,10 Moreover, their ubiquitous distribution in the aquatic biota including fish as well as marine birds and mammals spanning from tropical to Arctic waters has rasied great environmental concern.11−16 South China has now become a major global dumping site of electronic wastes, and concentrations of PBDEs in marine sediments in the region (>7340 ng g−1 dry wt) and its proximity, Hong Kong (up to 53.6 ng g−1 dry wt) are among the highest in the world.17,18 Moreover, PBDEs concentrations © 2012 American Chemical Society
Received: Revised: Accepted: Published: 7772
January 20, 2012 June 12, 2012 June 15, 2012 June 15, 2012 dx.doi.org/10.1021/es300261c | Environ. Sci. Technol. 2012, 46, 7772−7781
Environmental Science & Technology
Article
marine sediment in Hong Kong,17,19 (c) the possible adverse effects of BDE-47 on aquatic wildlife have raised increasing concern,4,8,28,29,31,50 and (d) bioaccumulation of BDE-47 in the marine mussel Mytilus edulis34,51 has been shown to severely damage the ovarian follicles and ovocytes.37
may affect production and metabolism of thyroid and sex hormones, resulting in reproductive impairments such as reduced sperm counts, delayed puberty, suppressed growth of reproductive organs and altered sex-dependent behavior.24−26 In fish, a wide range of toxic effects has been observed following PBDEs exposure, including inhibition of egg-laying, morphological abnormalities, altered swimming behavior, impaired cardiovascular function, delayed hatching, altered thyroid hormone levels, as well as reduced sperm count, growth rate and fecundity.27−32 Invertebrates that inhabit the coastal environments are particularly prone to PBDEs exposure, due to their proximity to sites of electronic wastes disposal and wastewater discharge.17−19 PBDEs contamination of shrimps, crabs, mussels, clams, and oysters have been widely reported in the coastal waters of Hong Kong, South China, Denmark, Greenland, and Singapore.17,22,23,33−35 Surprisingly, the effects of PBDEs on marine invertebrates remain virtually unknown. Limited data, however, showed that larval development of the marine copepod Acartia tonsa was inhibited when exposed to 13 000 ng BDE-47 L−1 for 5 days,36 and severely damaged ovarian follicles and ovocytes were found when female mussels (Mytilus edilus) were exposed to 1000 ng BDE-47 L−1 for 3 weeks.37 Recently, PBDEs were shown to alter the larval settlement behavior of soft-bottom dwelling marine polychaetes. While Polydora cornuta larvae avoided sediment spiked with 3 ng BDE-47 g−1 dry wt, settlement of Pseudopolydora vexillosa and Capitella sp. I larvae increased in the same sediment.8 Rocky intertidal communities are characterized by a higher species richness, productivity, energy flow and diversity and are very different from that of the soft sediment substratum. Substratum preference and subsequent settlement and growth of larvae may govern the structure and dynamics of intertidal communities.38 Furthermore, the mechanisms governing the larval settlement of these communities (determined by a variety of factors including bacterial density and community composition, and roughness and texture of substrates) are very different from those of soft-bottom dwelling faunas (primarily determined by organic content in sediment).39 It is well-known that the microbial composition of biofilms on hard substrates can dictate larval settlement of sessile invertebrates, including barnacles, polychaetes, bryozoans, oysters, and gastropods.39,40 It was demonstrated that pollution may alter the microbial composition on biofilms, thereby changing the larval settlement behavior and success.41,42 Using three model intertidal species accross three phyla, including the polychaete Hydroides elegans (Phylum Annelida), the gastropod Crepidula onyx (Phylum Mollusca), and the barnacle Balanus amphitrite (Phylum Arthopoda), this study set out to test the hypotheses that (a) chronic exposure throughout the whole larval stage to environmentally realistic concentrations and higher concentrations of PBDEs would affect settlement, development, and growth, and (b) PBDEs would change the bacterial community composition and abundance on biofilms, and hence alter the larval settlement response. The three species used in the present study are commonly used as models in genomics, proteomics, and ecotoxicology studies.43−49 BDE-47 was used as the model toxicant in this study because (a) it is the predominant PBDE congener found in the marine environment and biota worldwide,2,17,22,33−35 (b) it is one of the most abundant PBDE congeners reported in seawater and
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MATERIALS AND METHODS Larva Culture. Adults of Hydroides elegans, Crepidula onyx, and Balanus amphitrite were collected from the low intertidal zone at Yung Shue O (22°19′N, 114°16′E), the Victoria Harbour (22°17′N, 114°10′E), and Port Shelter (22°19′N, 114°16′E) of Hong Kong, respectively. Calcareous tubes of H. elegans were gently broken to induce spawning in Petri dishes containing membrane-filtered (pore size 0.22 μm) seawater. Eggs from multiple females were pooled together and mixed with sperm from only one male in order to reduce polyspermy.52 For C. onyx, egg capsules were located underneath the female foot and thousands of larvae were released after brooding for about two weeks.41 B. amphitrite embryos in the mature egg lamellae hatched into nauplius I, which were attracted to a point-source light and subsequently, collected using a pipet.53 Larval development of this barnalce species consists of six naupliar and one cypris stages. Nauplius I is nonfeeding and molts to nauplius II within 3 h of hatching. Effects of BDE-47 on Growth and Settlement of Hydroides elegans and Crepidula onyx Larvae. Effects of long-term, chronic exposure (i.e., 5 and 8 days for H. elegans and C. onyx, respectively) on larval growth and settlement were examined at five different concentrations of BDE-47 (0.1, 1, 10, 100, 1000 ng L−1). The lowest testing concentration (i.e., 0.1 ng L−1) was similar to the reported PBDEs concentration in seawater in the Pearl River Delta region.19 Stock solutions were prepared in advance by dissolving 1, 10, 100, 1000, or 10000 ng of BDE-47 in 1 mL of n-hexane and appropriate dilutions were made with filtered seawater. Blank and solvent controls were also included. An equal volume of n-hexane (0.01%) was used in all treatments and solvent control. Each control and treatment had three replicates, and each replicate consisted of approximately 200 larvae and 200 mL testing medium in a glass beaker (i.e., a total of 600 larvae in each treatment and control). The beakers were silylated by the silyating agent dichlorodimethylsilane prior to use, in order to minimize the adsorption loss of BDE-47. Larvae were reared at 25 °C, on a diet of I. galbana at 2 × 105 cells L−1 (by adding 2 mL algal solution that had an adjusted cell concentration to the beaker containing seawater, larvae and PBDEs). Testing medium was changed once daily and dead individuals removed. The mortality rate in each beaker over the entire exposure period was
