The lament of sediment: pesticide pollution hurts coastal biodiversity

Journal source: Pitacco, V. et al., Multiannual Trend of Micro-Pollutants in Sediments and Benthic Community Response in a Mediterranean Lagoon (Sacca di Goro, Italy) Water 2020, 12, 1074; doi:10.3390/w12041074

A day at the beach: you might enjoy a leisurely stroll by the shore, feeling the sand in between your toes. While you are taking in the crisp salty air, the same sands that tickle your feet may also harbor unwanted pollution. As coastal areas become increasingly developed and populated, urban and industrial wastes can make their way into marine waters, where they can accumulate within the sediments. Different types of pollutants, from pesticides to heavy metals, may enter these communities and stay in the sediments for various lengths of time. This is concerning, because not only are these pollutants dangerous to us, but they can also have adverse effects on the animal communities living within the sediments.

Nestled within these sands are a host of burrowing marine animals, like worms, mussels, snails, and a variety of crustaceans, which may be the first to be negatively impacted by these wastes. This sediment-dwelling community of animals is collectively termed the macrobenthos, and serves as a critical component of nearshore marine ecosystems. These critters serve as prime food sources for other marine animals such as fish. If contaminated sediments impair the macrobenthos, reverberating effects could be felt by animals higher up in the food web, which is concerning to scientists. Scientists need to monitor ecosystems that are at risk of receiving potentially toxic wastes in order to protect the species living there. 

One way that scientists can measure how much an ecosystem is impacted by pollution is by counting the number of species present at a given time. Healthy ecosystems with few pollutants tend to have more species than those that are degraded by human activities. In a polluted ecosystem, sensitive species may disappear entirely, while tolerant species may still hang on. When an ecosystem loses certain species, it may become less productive and unable to support other animals higher up in the food web. Therefore, scientists want to understand how different pollutants impact sediment animal communities.

Simplified diagram of how upstream human activities can send a multitude of pollutants into the coastal sediment communities. Photo credit: Katherine Barrett via BioRender.

Researchers Pitacco and colleagues from the National Institute of Biology in Slovenia investigated the different types of contamination present in the sediments of the Sacca di Goro, a Mediterranean lagoon on the northwest coast of Italy. They found that the sediments had more pollutants than is considered safe, and some contaminants like arsenic may be devastating for the coastal species.








Map of the study area in the Sacca di Goro lagoon. Photo credit: Pitacco et al. 2020.

The authors took sediment samples from this lagoon over a 6-year period, from 2004 to 2010, and studied how contaminant levels varied over time. They measured the concentrations of pesticides and trace metals, including arsenic, copper, and lead. They also measured levels of polycyclic aromatic hydrocarbons, a group of toxic compounds produced from various industries.

During this study, the authors also sampled the sediments to identify the species living there, and to determine if contaminant levels had an effect on the number of species. 

What did they find?

The authors found that the sediments had more trace elements, in particular lead, nickel, and cadmium,  had more trace elements, in particular lead, nickel, and cadmium, than the Italian government considers safe. They also found pesticides, including the infamous pesticide DDT and its breakdown product DDE, which all also exceeded the Italian national safety theshold. 

Pollution- tolerant species dominated sediment communities, especially worms called Streblospio shrubsolii. In contrast, sensitive species, which included amphipods (side-swimmers), were present only in low numbers.  There weren’t many pollution-sensitive species. In fact, the authors reported that the number of species declined as the concentration of arsenic and DDE increased. 

The bigger picture

This study showed that pollutants originating from industry, cropland, and urban development, which at first glance all seem at a distance from the ocean, can actually damage the ecology and habitat of the same places we actively seek out for enjoyment and recreation. Unfortunately, pollutants are ubiquitous in this modern age, especially in our own households. The chemicals we spray on our yards washes away with rain and ends up in the creeks and streams that flow through our neighborhoods, eventually meeting up with the open sea. In addition to showing how pollution can upset healthy sediment communities, this study also sheds light on the importance of considering the far-reaching and often unintentional negative impacts of human activities on marine food webs.

Perhaps, going forward, industries can implement preventative measures to reduce the output of wastes that may harm marine life. Hopefully, then, in the future, long-term monitoring will show a rebound in species numbers as these ecosystems recover from upland pollution.

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