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Microplastics are a widespread environmental contaminant that raises serious concern for aquatic organisms. Hence, the present study was conducted to investigate the spatial and seasonal variation of microplastics, their characteristics, polymer types and the risk assessment caused by the microplastics in six sampling sites along the Thoothukudi region. The average microplastic abundance ranged from 32 ± 26 to 232 ± 229 items/kg and 54 ± 41 to 619 ± 377 items/l in sediment and surface water, respectively, and they exhibited a significant spatial difference among the sampling sites. The microplastic abundance also showed a significant difference among the seasons with the monsoon significantly recording the highest mean microplastic abundance in sediment (160 ± 130 items/kg) and surface water (454 ± 374 items/l). In sediment and surface water, fragment (sediment: 52.72%, surface water: 40.89%), 0.5-1 mm (sediment: 43.96%, surface water: 31.11%) and blue-coloured (sediment: 52.33%, surface water: 41.85%) microplastics were dominant with no significant difference both spatially and seasonally. Polyethylene, the dominant polymer, was observed in both the sediment and surface water, accounting for about 47.58% and 49.83%, respectively, and it showed no significant difference among the selected sites. This signifies that they are homogenously distributed along the coast and further suggests that these particles persisted in the sediment and surface water for a longer period of time. The results of the polymer hazard index show that the sediment (PHI = 1181.63) and surface water (PHI = 1018.66) were severely contaminated (hazard level V) with microplastic polymers such as PE, PP, PS, PET and PA. It was also found that the degree of the microplastic contamination in sediment (PLI = 3.57) and surface water (PLI = 3.84) was lower (hazard level I). The overall risk index (RI) for sediment (253.48) and surface water (444.74) falls under the higher risk category. From the correlation analysis, a significantly positive relationship was observed between microplastics in sediment and surface water based on each classification (abundance, shape, size, colour and polymer). This suggests that microplastics rejoin the water column from the sediment through resuspension, which occurs due to the circulation, tides and sedimentation rate. This might be the reason for the higher microplastic abundance in the surface water than in the sediment. As a result, proper management measures to reduce plastic waste disposal in the marine environment should be implemented to lessen the effects of microplastics on marine biota and on public health.

In this study, a multiplex PCR assay was developed for the authentication of three commercially important shrimp species viz., Penaeus monodon, Penaeus vannamei, and Penaeus indicus. Three new species-specific primers designed from the mitochondrial 16S rRNA gene yielded distinct amplicon size of 360, 277, and 203 bp for P. monodon, P.vannamei, and P.indicus, respectively. The sensitivity, accuracy, specificity, and suitability of the multiplex PCR assay was determined as per standard protocol. The assay exhibited high specificity to the target shrimp species. The sensitivity ranged from 1 to 0.1 ng/μl of DNA concentration. In-house validation with eleven types of mixed-species gave 100% correlation in the authentication of the target shrimp species. Field validation with 22 processed commercial shrimp products revealed 22% mislabeling. The developed multiplex PCR assay authenticated the three commercially important Penaeids in processed shrimp products from other related shrimp, fish as well as crab species in a single run.

Five species of macroalgae, namely Sargassum wightii, Padina tetrastromatica, Ulva lactuca, Caulerpa racemosa and Gracilaria edulis collected from three sampling sites, viz. Harbour Beach (site 1), Tharuvaikkulam (site 2) and Hare Island (site 3), situated along the Thoothukudi region of the Gulf of Mannar were analysed for 17 organochlorine pesticides (OCPs) by gas chromatography-mass spectrometry (GC-MS) to assess their suitability as biomonitors of pesticide contamination. The total OCP concentrations were several folds higher in all the macroalgae collected from site 1 than in the other two sites. Brown alga S. wightii accumulated more OCPs (297 ng g-1) than the other sampled algal species in site 1. The OCPs assessed in this study were endrin aldehyde (51 ng g-1), endrin (48 ng g-1), β hexachlorocyclohexane (45 ng g-1), heptachlor epoxide (43 ng g-1), dichlorodiphenyldichloroethylene (37 ng g-1) and endosulfan sulfate (11 ng g-1) in S. wightii. It was observed that the green alga C. racemosa had selective sorption of endosulfan I (43 ng g-1) and red alga G. edulis had selective sorption of endosulfan II (44 ng g-1). The ability of seaweeds to accumulate pesticides was found to be species specific and not class specific. The study indicated that S. wightii could be used as a biomonitor of OCP residues in the marine environment, with the exception of endosulfan. Keywords: Endosulfan, Macroalgae, OCPs, Pesticides

Organochlorine pesticides (OCPs) in the edible red seaweeds viz. Gracilaria verrucosa and Gelidiella acerosa, collected from four sites viz. Thoothukudi (1), Earvadi (2), Seeniyappa Dhargah (3) and Rameswaram (4) of Gulf of Mannar were assessed. Total OCP residues in G. acerosa ranged from 6 ngg−1 to 508 ngg−1 and in G. verrucosa from 0.36 ng g−1 to 270.41 ng g−1. The OCP residues were maximum in G. acerosa of Rameswaram and in G. verrucosa of Seeniyappa Dhargah. The OCP residues were high in the month January, which coincided with the fruiting season of seaweeds. The major OCPs in red seaweeds recorded were HCH, endosulfan, aldrin, endrin and DDT and their mean concentration was 6.864 ngg−1, 79.107 ng g−1, 1.16 ng g−1, 0.97 ng g−1 and 13.66 ng g−1, respectively. Specific accumulation of endrin residues by G. acerosa is a distinct feature. In terms of pesticide toxicity, it is inferred that the red seaweeds collected immediately after the rainy season contained high OCP residues and shall not be safe for consumption.