15.1: Lab 15 Background

Learning Objectives

• Explain the connection between life and plastics in the environment.
• Isolate and identify the composition of unknown plastics pieces from sand.
• Predict the effects of overharvesting on fish populations.
• Explain the ecological and economic benefits of sustainable fishing.

Introduction: Plastics

Sand is made of tiny rock grains created by erosion from the land. While, plastic is a man-made material that is melted, shaped, and cooled. Most plastics are made from petroleum (also called fossil fuels and is similar to the gasoline that goes into our cars). Petroleum fuels are a limited resource on the planet and their extraction creates other environmental issues such as increasing carbon emissions. To make plastic products, the fuel must first be extracted from deep within the earth’s crust. Then it is processed into a polymer, which is a long chain molecule of many repeating sections. When these polymers are connected, they will begin to form a solid plastic. Most commonly, the companies produce resin pellets, which are tiny beads of plastic that can be melted down and molded into any shaped object. The pellets are then purchased by molding companies who work with various brands to make their bottles, bags, or other products.

There are many types of plastics. Type 1 PETE polyethylene terephthalate is found in water bottles. Type 2 HDPE high-density polyethylene is found in milk jugs and grocery store bags. Type 3 PVC polyvinyl chloride is found in clear food packaging and shampoo bottles. Type 4 LDPE low-density polyethylene is found in squeeze bottles, bread bags, and some food bags. Type 5 polypropylene is found in bottle caps, straws, and medicine bottles. Type 6 polystyrene is found in Styrofoam, disposable utensils, and cups. Certain molecules can be added to change the properties of the plastic such as increasing hardness, making it more bendable, or improving flame resistance. The addition of these other substances commonly makes the plastic non-recyclable. Also, each different type of plastic is recycled in a unique way.

Generally speaking, plastic products are not currently recycled and are definitely not recycled at the rate they are produced. Most plastics even when put into the recycling bins are never reused. One example is plastic wrap used to store foods cannot be recycled because they are too thin and get caught in the separating machines. Another example is plastic chip bags cannot be recycled because they also contain aluminum foil on the inside that cannot be taken apart from the plastic exterior. Small plastic items like toothbrushes, tampon exteriors, eating utensils, twist ties for bread, straws, and many others are all too small and get caught in the sorting machines. Deodorant containers and yogurt cups are made of multiple types of plastic that cannot be separated so neither is recyclable. Water, soda, and other beverage bottles are the most commonly recycled items. They are large enough and generally made of only one type of plastic. Some bottles have a different type of lid that is recommended to be removed prior to recycling. Other bottles like shampoo, peanut butter, and condiments are also recyclable but need to be cleaned prior to throwing them away.

When items don’t get recycled, there is the possibility of them ending up in our environment. Historically, other countries bought plastic trash from the United States. Some of those countries would try to reuse items that they could and others burned the materials as an energy source. Burning plastic is not a great option because it produces many toxic chemicals. Ultimately, loads of plastic are ending up in the oceans. One reason is that many plastics are simply not meant to be recycled. These plastics then end up in landfills that possibly pollute the nearby waterways. Then the plastic floats along eventually reaching the ocean. When plastic is exposed to the sun for long periods of time, the sunlight causes the plastics to break down into smaller pieces, a process called photodegradation. Scientists are finding that the large plastic objects are breaking down into microplastics that are smaller than 5mm and hard to see with the naked eye, making them challenging to track. Even more challenging to track is when the plastics break down into nanoplastics, which are smaller than 1mm and need to be chemically tested for because they cannot be seen.

Plastics are an incredibly useful tool in modern society. Plastics are lightweight, colorless, and durable. They are essential in the medical field where diseases could spread if other materials are used. Plastics keep our foods fresher for longer. The goal of today’s lab is to learn about plastics, identify the types of plastics found in our local beach sand, and discuss this issue. This lab is not meant to shame anyone for their use of plastic. It is also not trying to convince anyone to switch to using non-plastic alternatives. While working through these exercises, keep an open mind and considerate tone during discussions.

Introduction: Population Ecology

The field of ecology can be studied at many different scales. Population ecology studies the changes to a population’s size and demographics. Community ecology studies interactions between species. Ecosystem ecology measures environmental effects, such as energy and nutrient cycling, on populations and communities. Applied ecology attempts to apply the different kinds of ecology to real world problems. For example, conservation ecology works to protect vulnerable, threatened, or endangered species from extinction. As we may have noticed, many of these fields of ecology overlap and are also interdisciplinary with other fields of study such as evolution, physiology, chemistry, physics, and more.

In this lab, we will apply the principles of population ecology to determine how we might be able to manage fish populations more sustainably. A population is a group of individuals of the same species interacting in a common area. The population size is the number of individuals in the population, and population growth measures how much the population size changes over time. It is important to note that, in this case, the term growth measures both the increase in population size (positive growth) and decrease in population size (negative growth). Population ecologists attempt to determine the main factors that affect population growth.

Commercial fishing operations harvest many thousands of tons of fish each year. Seafood is an important source of nutrition for many human populations, including here in southern California. When done responsibly, commercial fishing can feed humans and provide people with income; while leaving enough fish in the sea to both sustain other predators and allow the harvested species to repopulate. This is the goal of sustainable fishing. However, many species of fish have been, and continue to be, overharvested. Some commercial fishing vessels use large nets, called drift nets. Drift nets were widely used throughout the 20th century and could be as long as 50km (31mi)! Vessels could harvest thousands of tons of fish at a time leading to the decline, and in some cases complete collapse, of various fish species. Drift nets also cause significant amounts of bycatch, which is when non-target species are caught in the large nets. Bycatch has significantly contributed to the decline in global populations of sensitive species like sea turtles and dolphins. As a result, in 1987, the United States limited drift nets to 2.8km (1.7mi) when used in American waters. The United Nations agreed to similar limitations in international waters. Other commercial fishing practices cause similar ecological damage. For example, bottom trawling tows large nets along the ocean floor, allowing for similar levels of harvesting and bycatch, but also damages sensitive ocean floor ecosystems that may take long periods of time to recover. Recent focus on sustainable fishing practices is helping to maintain healthy fish populations, but much work still needs to be done to ensure the longevity of fish populations. This lab, which is adapted from Biol 213 at CSULB, will simulate both the economic and biological aspects of commercial fishing.