1 Introduction

Marine litter consists of items that have been deliberately discarded, unintentionally lost or transported by winds and rivers, into the sea and on beaches [1]. Based on this concept, it is not difficult to understand why plastic products conform most of the waste found in oceans [2]. Plastic products are often incorrectly disposed [3, 4] at end of life (EoL), worsened by the lack of economic value as waste [5, 6]. In addition to collection and sorting difficulties, this economic condition discourages plastic waste flows to circulate in the current recycling schemes. Plastic are easily transported into nature due to general product characteristic, e.g. lightweight, small-sized and the float potential. Consequently, plastic waste may reach oceans via inland waterways, wastewater outflows and transport by wind or tides [7].

Statistical researchers endorse this scenario. In the European Union, 80–85% of marine litter, measured as beach litter counts, is plastic, with single-use plastic items representing 50% and fishing-related items representing 27% of the total [8]. Estimates based on 192 coastal countries pinpoint that from 31.9 million MT of mismanaged plastic in 2010, 4.8 to 12.7 million MT entered the ocean [7]. However, despite the significant values raised by these references, which indicates a constant accumulation over the decades, the issue gained prominence only in the last years, when global society started to worry about the effects of marine litter, mainly due to its impacts over marine biodiversity.

The disposable plastic drinking straw may be indicated as the most representative flagship of this current society’s concern. It has been a hot topic since 2015, after a video showing a drinking straw stuck in a sea turtle’s nose [9]. Since then, this product turned into the image of marine litter problem and boosted by society’s opinion about the situation, propelled a large movement to eliminate plastic straws from our daily lives [10,11,12,13,14,15].

There are two aspects of this situation that became clear since 2015: (a) the overall movement had positive influence on marine litter waste problem recognition and (at some extension) on directing efforts to solve it, and (b) with laws, policies and prohibitions, alternative solutions as reusable straws or specially designed cup lids that perform the same function, gained prominence. However, despite the common intention to deal with plastic waste on the oceans, alternative scenarios may suffer with trade-off conditions as pointed by [6, 16, 17], whereas the simple prohibition without the proper scientific validation may cause rebound effects in medium to long terms (e.g. increase climate change).

Life Cycle Assessment (LCA) is able to identify this trade-off conditions between different scenarios [18,19,20,21] being recognized as a trustworthy, scientific and understandable approach that uses several mathematical models to address sustainability aspects of human activities [22,23,24]. However, it currently lacks a marine impact focus and robust models to account for the environmental effects of leakage into the natural environment [5, 25] especially related to the Life Cycle Impact Assessment (LCIA) framework [25,26,27]. On top of that, current EoL scenarios dealing with plastic waste on LCA , as sanitary landfilling, are not well addressed by impact category mechanisms due to specific product characteristics (low degradability; impacts are predominantly physical but may be also biological/chemical thorough the years) and the difficulties reproducing such complex cause-effect chains in a mathematic model. As an effect in these cases, LCA can produce some asymmetry that can lead into a misleading decision-making with not carefully considered premises and critical analysis over modelling.

Consequently, there is a major gap between scientific research and the environmental technical analysis related to “what is happening” in marine ecosystems. While this bridge is not built, this gap is being fulfilled by society judgement over the theme.

Society has built an opinion about this theme based on important evidences, although empirical and anecdotal, in most cases, on the impacts plastic can cause in marine environment. However, there is still lack of scientific development to assure the real magnitude of the damage or to trace the cause-effect pathway. Nevertheless, public policies established worldwide based only in this perception may not comprise the whole picture and may be potentially subject to failure, for example, promoting environmental trade-offs between life cycle stages or different product alternatives. Thus, the aim of this paper is to provide insights to this discussion by calculating the impact factor that is addressed to the LCA score by a new impact category based on society’s perception on marine litter.

2 Material and Methods

A comparative LCA ISO compliant (i.e. LCA conducted by a LCA consulting company and reviewed by an independent third-part reviewer institution) [19, 28] was performed to assess five different drinking straws, representatives of the main commercial one-way and reusable alternatives available in the Brazilian market in 2018. However, for the sake of brevity, only plastic (marine litter case related) and stainless steel (best LCA score within reusable alternatives) options are presented since they are also the base case study of this paper. Boundaries were stablished from cradle to grave for the functional unit (FU) of “to drink 300 ml of a generic liquid from a regular glass”. Their main characteristics and simplified scenario scoping are presented in Table 1.

Table 1 Main characteristics of product systems under analysis
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The foreground data regarding raw materials weight is from primary sources, measured through a gravimetric procedure by precision scale on real (acquired) products, including primary packaging and additional elements. For raw material acquisition and material transformation, data were gathered exclusively from secondary sources such as the ecoinvent® database version 3. The washing step of stainless steel straw represents a manual and domestic process, representing an average of ten processes measured in loco for water and washing agent consumptions and effluent generation. EoL flows (including straws, packaging and complimentary elements) represent raw materials consumption based on mass balances, whereas landfilling was based on secondary data from literature and ecoinvent® database version 3.

A hybrid LCIA method based on IPCC [32], CML-IA [33] and ReCiPe 2008 at the midpoint level [34] was adopted with addition to an LCI-based impact category related to land use. Normalization was based on CML-IA divided by world population for ozone depletion, photochemical oxidation and eutrophication; CML non-baseline divided by world population for acidification; CML 2 divided by world population for resource consumption; ReCiPe divided by world population for climate change; and ILCD for respiratory inorganics and an estimated factor for land use. Weighting factors were defined based on major Braskem stakeholder’s opinion, including company representatives, society and external specialists. The impact categories, characterization methods and normalization (N. factors) and weighting factors (W. factors) are listed in Table 2.

Table 2 LCIA single score method (characterization , normalization and weighting)
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From the single score (SS) LCA results, we proposed a new impact category, namely, marine litter. This category aims to represent the society perception regarding the presence of plastic debris on the oceans, and, therefore, does not represent the traditional bottom-up approach that defines, scientifically, the cause-effect pathway (LCA characterization models). The rationale in this paper’s proposal considers that characterization factor could be derived from top-down strategy (Fig. 1), based on the premise that society perception on this matter is correct.

Fig. 1
figure 1

Different approaches for characterization factor definition

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From this perception, overall LCA SS of plastic systems should be, at least, equally environmentally harmful than other alternatives. When this condition is not respected, the final LCA value gap is, therefore, attributed to the marine litter impact category representing society perception, as illustrated in Fig. 2.

Fig. 2
figure 2

Marine litter characterization factor mathematical concept (in compliance with the amount of plastic waste generated and their risk of becoming litter)

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3 Results and Discussions

3.1 Life Cycle Assessment of Drinking Straws

Each product system has a specific behaviour in terms of LCI as shown in Table 3. Plastic drinking straws (one-way product) have simple packaging, consisting of LDPE films (0.09 g) that are discarded directly during the use phase. Stainless steel drinking straw (reusable product) has a carrying bag (made of woven cotton) to accommodate both the straw and the cleaning brush. Similarly to the reusable straw, these elements are influenced by reuse rate, having their inputs diluted to fill the FU . In the use phase, stainless steel straw presuppose a washing phase, where water (with 600 ml of tap water) and a washing agent (1 g of linear alkyl sulfonate, LAS detergent) are consumed. At last, EoL stage is represented by output flows in accordance with mass balance over the previous life cycle steps. Therefore, reusable straws have lower solid wastes than one-way straws, but on the other hand, they have a significant liquid effluent generated during the washing process (use phase).

Table 3 Drinking straws Life Cycle Inventory (LCI)
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Within the LCA scoping of this paper, single score results show a better environmental performance for plastic drinking straw with lower impacts (31.3μPt) if compared to stainless steel drinking straw (393.2μPt), as depicted by Fig. 3. Climate change, respiratory inorganics and resource depletion (water) are the main contributors to the final single score of both drinking straws with the major difference in terms of values related to the water consumption, followed by impacts due to respiratory effects.

Fig. 3
figure 3

Single score LCA results

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Raw material acquisition (i.e. PP production/pellet), commonly a hotspot for one-way plastic LCA [37, 38], is the main driver for all impact categories in the case of the plastic drinking straw. Stainless steel straw has hotspots positioned mainly in additional element production (woven cotton and wired tin), detergent production and tap water consumption (during washing process). Those conditions turn the stainless steel straw into a worst environmental choice than plastic drinking straw, with its production (including mining and steel processing) and EoL being significantly diluted by reuse rate. Similar results are shown by [37, 39, 40].

3.2 Society’s Perception-Based Characterization Factor

Assuming that the difference of 362 μPt between the SS results from Fig. 3 should be attributed to the plastic drinking straw final disposal flow, according to the equation in Fig. 2, we can estimate the marine litter characterization factor as 860 μPt per gram of mismanaged polymer (assuming that 100% of polymer consumption in the plastic drinking straw life cycle becomes marine litter). Comparing the impact estimated for the final disposal flow with the PP production demonstrates that this factor represents an increase of 1048% (Fig. 4). This means that the mismanaged flow represents an impact 10.5 times higher compared to the polypropylene upstream chain (i.e. equivalent to 1 order of magnitude). If we assume that 3% of the world’s plastic production ends up in the oceans [7], the characterization factor would increase up to 28722 μPt per g of mismanaged plastic. In this case, the environmental impact assigned to marine litter would represent 363 times more than its own production (a difference of 2.6 orders of magnitude).

Fig. 4
figure 4

Perspective of the magnitude of the new impact characterization factor considering 100% of plastic as marine litter

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Analysing the results with a different perspective based on the normalization and weighting factors of the Braskem’s LCIA method for the climate change category, the impact of plastics in the ocean would be equal to 2.2E-2 kg of CO2 eq. This result represents an impact 20 times higher than the total plastic drinking straw life cycle emissions (1.04E-3 kg CO2 eq. or 18 μPt) to perform the FU when correctly disposed in a landfill.

4 Conclusions

According to LCA results, polymer-based solutions tend to have better environmental performance when compared to the stainless steel reusable alternative, if correctly disposed. While reusable options heavily depend on consumers’ behaviour at use phase, polymer single-use option is dependent of consumers’ behaviour at end-of-life step.

The lack of characterization factors to account for the potential impacts exerted by plastics in the natural environment, mainly those in the ocean, indirectly turns the society’s perception of the problem, the qualitative measure of the “characterization factor” for the marine litter impact category, without a sound scientific basis.

When attributing this perception on the results of a comparative LCA of drinking straws, following the rationale of society’s perspective for marine litter, the impact of mismanaged plastics can potentially represent 10.5 and 363 times greater than its own production impacts if 100% and 3% of the plastic are considered marine litter, respectively. In both situations, the value seems to be overrated.

Other perspective, based on the climate change at midpoint LCIA level, indicates that it would be necessary 20 times more CO2 equivalent emissions only to equalize the single score results of 0.42 g of mismanaged plastic. In both cases, LCA results due to characterization factor based on public opinion seem to be significantly higher and unbalanced with the other life cycle stages of the plastic drinking straw. Thus, society does not perceive the impacts of the polymer straw application as LCA results may indicate, mainly in order of magnitude.

Even though this work’s aim is to present a case as an exercise and not to properly calculate a reproducible characterization factor, it gives insight about the current LCA gap of knowledge and how far an LCA result may be from public opinion. Doubtlessly science should not be nudged by any perception, and real characterizations factors are still to be calculated. The lack of data, high complexity of the subject, and the difficulty of proper communication between scientific community and social influencers tend to lead people to the precautionary side and to make decisions with no data to support. In this case, society becomes very prone to suffer from rebound effects.